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How do I abort a socket.recv() from another thread in Python
Question: I have a main thread that waits for connection. It spawns client threads that
will echo the response from the client (telnet in this case). But say that I
want to close down all sockets and all threads after some time, like after 1
connection. How would I do? If I do clientSocket.close() from the main thread,
it won't stop doing the recv. It will only stop if I first send something
through telnet, then it will fail doing further sends and recvs.
My code look like this:
# Echo server program
import socket
from threading import Thread
import time
class ClientThread(Thread):
def __init__(self, clientSocket):
Thread.__init__(self)
self.clientSocket = clientSocket
def run(self):
while 1:
try:
# It will hang here, even if I do close on the socket
data = self.clientSocket.recv(1024)
print "Got data: ", data
self.clientSocket.send(data)
except:
break
self.clientSocket.close()
HOST = ''
PORT = 6000
serverSocket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
serverSocket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
serverSocket.bind((HOST, PORT))
serverSocket.listen(1)
clientSocket, addr = serverSocket.accept()
print 'Got a new connection from: ', addr
clientThread = ClientThread(clientSocket)
clientThread.start()
time.sleep(1)
# This won't make the recv in the clientThread to stop immediately,
# nor will it generate an exception
clientSocket.close()
Answer: I know this is an old thread and that Samuel probably fixed his issue a long
time ago. However, I had the same problem and came across this post while
google'ing. Found a solution and think it is worthwhile to add.
You can use the shutdown method on the socket class. It can prevent further
sends, receives or both.
> socket.shutdown(socket.SHUT_WR)
The above prevents future sends, as an example.
[See Python docs for more
info.](http://docs.python.org/py3k/library/socket.html?highlight=socket#socket)
|
Python: What is the hard recursion limit for Linux, Mac and Windows?
Question: Python's `sys` module [provides a
function](http://docs.python.org/library/sys.html#sys.setrecursionlimit)
`setrecursionlimit` that lets you change Python's maximum recursion limit. The
docs say:
> The highest possible limit is platform-dependent.
My question is: What is the highest possible limits for various platforms,
under CPython? I would like to know the values for Linux, Mac and Windows.
**UPDATE:** Can we please avoid "You're doing it wrong" answers? I know that
trying to do very deep recursion is usually a bad idea. I've considered the
pros and cons in my specific situation and decided that I want to do it.
Answer: On Windows (at least), `sys.setrecursionlimit` isn't the full story. The hard
limit is on a per-thread basis and you need to call `threading.stack_size` and
create a new thread once you reach a certain limit. (I think 1MB, but not
sure) I've used this approach to increase it to a 64MB stack.
import sys
import threading
threading.stack_size(67108864) # 64MB stack
sys.setrecursionlimit(2 ** 20) # something real big
# you actually hit the 64MB limit first
# going by other answers, could just use 2**32-1
# only new threads get the redefined stack size
thread = threading.Thread(target=main)
thread.start()
I haven't tried to see what limits there might be on `threading.stack_size`,
but feel free to try... that's where you need to look.
In summary, `sys.setrecursionlimit` is just a limit enforced by the
interpreter itself. `threading.stack_size` lets you manipulate the actual
limit imposed by the OS. If you hit the latter limit first, Python will just
crash completely.
|
How do I do this in Python (File Manipulation)?
Question: I have a bunch of HTML files in HTML folder. Those HTML files have unicode
characters which I solved by using `filter(lambda x: x in string.printable,
line)`. Now how do I write the changes back to the original file? What is the
best way of doing it? Each HTML file is of 30 kb in size.
1 import os, string
2
3 for file in os.listdir("HTML/"):
4 print file
5 myfile = open('HTML/' + file)
6 fileList = myfile.readlines()
9 for line in fileList:
10 #print line
11 line = filter(lambda x: x in string.printable, line)
12 myfile.close()
Answer: Use the [fileinput](http://docs.python.org/library/fileinput.html#module-
fileinput) module. It allows you to read and write to the same file in place:
import fileinput,sys,os
files=[os.path.join('HTML',filename) for filename in os.listdir("HTML/")]
for line in fileinput.input(files, inplace=True):
line = filter(lambda x: x in string.printable, line)
sys.stdout.write(line)
|
What is a simple fuzzy string matching algorithm in Python?
Question: I'm trying to find some sort of a good, fuzzy string matching algorithm.
Direct matching doesn't work for me — this isn't too good because unless my
strings are a 100% similar, the match fails. The
[Levenshtein](http://en.wikipedia.org/wiki/Levenshtein_distance) method
doesn't work too well for strings as it works on a character level. I was
looking for something along the lines of word level matching e.g.
> String A: The quick brown fox.
>
> String B: The quick brown fox jumped over the lazy dog.
>
> These should match as all words in string A are in string B.
Now, this is an oversimplified example but would anyone know a good, fuzzy
string matching algorithm that works on a word level.
Answer: I like [Drew's answer](http://stackoverflow.com/questions/2923420/fuzzy-
string-matching-algorithm-in-python/2923488#2923488).
You can use [difflib](http://docs.python.org/library/difflib.html) to find the
longest match:
>>> a = 'The quick brown fox.'
>>> b = 'The quick brown fox jumped over the lazy dog.'
>>> import difflib
>>> s = difflib.SequenceMatcher(None, a, b)
>>> s.find_longest_match(0,len(a),0,len(b))
Match(a=0, b=0, size=19) # returns NamedTuple (new in v2.6)
Or pick some minimum matching threshold. Example:
>>> difflib.SequenceMatcher(None, a, b).ratio()
0.61538461538461542
|
What's a good equivalent to python's subprocess.check_call that returns the contents of stdout?
Question: I'd like a good method that matches the interface of `subprocess.check_call`
\-- ie, it throws `CalledProcessError` when it fails, is synchronous, &c --
but instead of returning the return code of the command (if it even does that)
returns the program's output, either only stdout, or a tuple of (stdout,
stderr).
Does somebody have a method that does this?
Answer: ### Python 2.7+
from subprocess import check_output as qx
### Python < 2.7
From [subprocess.py](http://hg.python.org/cpython/file/2.7/Lib/subprocess.py):
import subprocess
def check_output(*popenargs, **kwargs):
if 'stdout' in kwargs:
raise ValueError('stdout argument not allowed, it will be overridden.')
process = subprocess.Popen(stdout=subprocess.PIPE, *popenargs, **kwargs)
output, unused_err = process.communicate()
retcode = process.poll()
if retcode:
cmd = kwargs.get("args")
if cmd is None:
cmd = popenargs[0]
raise subprocess.CalledProcessError(retcode, cmd, output=output)
return output
class CalledProcessError(Exception):
def __init__(self, returncode, cmd, output=None):
self.returncode = returncode
self.cmd = cmd
self.output = output
def __str__(self):
return "Command '%s' returned non-zero exit status %d" % (
self.cmd, self.returncode)
# overwrite CalledProcessError due to `output` keyword might be not available
subprocess.CalledProcessError = CalledProcessError
See also [Capturing system command output as a
string](http://stackoverflow.com/questions/236737/capturing-system-command-
output-as-a-string/236909#236909) for another example of possible
`check_output()` implementation.
|
How to debug ctypes call of c++ dll?
Question: in my python project I call a c++ dll using ctypes library. That c++ dll
consists on a wrapper dll that calls methods of a c# com interop dll.
Sometimes I have a COM exception. I like to see what it corresponds exactlly
but I don't know how to do it?
How can I attach the c++ debugger to this situation?
Thanks in advance
Answer: I don't know about your direct question, but maybe you could get around it by
using [comtypes](http://sourceforge.net/projects/comtypes/) to go straight
from COM to Python instead sticking C++ in between.
Then all you have to do is:
>>> from comtypes import client, COMError
>>> myclassinst = client.CreateObject('MyCOMClass.MyCOMClass')
>>> try:
... myclassinst.DoInvalidOperation()
... except COMError as e:
... print e.args
... print e.hresult
... print e.text
...
(-2147205118, None, (u'MyCOMClass: An Error Message', u'MyCOMClass.MyCOMClass.1', None, 0, None))
-2147205118
None
|
dynamic module creation
Question: I'd like to dynamically create a module from a dictionary, and I'm wondering
if adding an element to `sys.modules` is really the best way to do this. EG
context = { a: 1, b: 2 }
import types
test_context_module = types.ModuleType('TestContext', 'Module created to provide a context for tests')
test_context_module.__dict__.update(context)
import sys
sys.modules['TestContext'] = test_context_module
My immediate goal in this regard is to be able to provide a context for timing
test execution:
import timeit
timeit.Timer('a + b', 'from TestContext import *')
It seems that there are other ways to do this, since the Timer constructor
takes objects as well as strings. I'm still interested in learning how to do
this though, since a) it has other potential applications; and b) I'm not sure
exactly how to use objects with the Timer constructor; doing so may prove to
be less appropriate than this approach in some circumstances.
### EDITS/REVELATIONS/PHOOEYS/EUREKAE:
1. I've realized that the example code relating to running timing tests won't actually work, because `import *` only works at the _module_ level, and the context in which that statement is executed is that of a _function_ in the `testit` module. In other words, the globals dictionary used when executing that code is that of `__main__`, since that's where I was when I wrote the code in the interactive shell. So that rationale for figuring this out is a bit botched, but it's still a valid question.
2. I've discovered that the code run in the first set of examples has the undesirable effect that the namespace in which the newly created module's code executes is that of the module in which it was _declared_ , **_not_** _its own module_. This is like way weird, and could lead to all sorts of unexpected rattlesnakeic sketchiness. So I'm pretty sure that this is **not** how this sort of thing is meant to be done, if it is in fact something that the Guido doth shine upon.
3. The similar-but-subtly-different case of dynamically loading a module from a file that is not in python's include path is quite easily accomplished using `imp.load_source('NewModuleName', 'path/to/module/module_to_load.py')`. This does load the module into `sys.modules`. However this doesn't really answer my question, because really, what if you're running python on an [embedded platform with no filesystem](http://thedailywtf.com/Articles/The-cbitmap.aspx)?
I'm battling a considerable case of information overload at the moment, so I
could be mistaken, but there doesn't seem to be anything in the `imp` module
that's capable of this.
But the question, essentially, at this point is how to set the global (ie
module) context for an object. Maybe I should ask that more specifically? And
at a larger scope, how to get Python to do this while shoehorning objects into
a given module?
Answer: Hmm, well one thing I can tell you is that the `timeit` function actually
executes its code using the module's global variables. So in your example, you
could write
import timeit
timeit.a = 1
timeit.b = 2
timeit.Timer('a + b').timeit()
and it would work. But that doesn't address your more general problem of
defining a module dynamically.
Regarding the module definition problem, it's definitely possible and I think
you've stumbled on to pretty much the best way to do it. For reference, the
gist of what goes on when Python imports a module is basically the following:
module = imp.new_module(name)
execfile(file, module.__dict__)
That's kind of the same thing you do, except that you load the contents of the
module from an existing dictionary instead of a file. (I don't know of any
difference between `types.ModuleType` and `imp.new_module` other than the
docstring, so you can probably use them interchangeably) What you're doing is
somewhat akin to writing your own importer, and when you do that, you can
certainly expect to mess with `sys.modules`.
As an aside, even if your `import *` thing was legal within a function, you
might still have problems because oddly enough, the statement you pass to the
`Timer` doesn't seem to recognize its own local variables. I invoked a bit of
Python voodoo by the name of `extract_context()` (it's a function I wrote) to
set `a` and `b` at the local scope and ran
print timeit.Timer('print locals(); a + b', 'sys.modules["__main__"].extract_context()').timeit()
Sure enough, the printout of `locals()` included `a` and `b`:
{'a': 1, 'b': 2, '_timer': <built-in function time>, '_it': repeat(None, 999999), '_t0': 1277378305.3572791, '_i': None}
but it still complained `NameError: global name 'a' is not defined`. Weird.
|
Setting System.Drawing.Color through .NET COM Interop
Question: I am trying to use Aspose.Words library through COM Interop. There is one
critical problem: I cannot set color. It is supposed to work by assigning to
DocumentBuilder.Font.Color, but when I try to do it I get OLE error
0x80131509. My problem is pretty much like [this
one](http://www.aspose.com/community/forums/81588/font.color/showthread.aspx#81588).
update:
Code Sample:
from win32com.client import Dispatch
Doc = Dispatch("Aspose.Words.Document")
Builder = Dispatch("Aspose.Words.DocumentBuilder")
Builder.Document = Doc
print Builder.Font.Size
print Builder.Font.Color
Result:
12.0
Traceback (most recent call last):
File "aaa.py", line 6, in <module>
print Builder.Font.Color
File "D:\Python26\lib\site-packages\win32com\client\dynamic.py", line 501, in __getattr__
ret = self._oleobj_.Invoke(retEntry.dispid,0,invoke_type,1)
pywintypes.com_error: (-2146233079, 'OLE error 0x80131509', None, None)
Using something like Font.Color = 0xff0000 fails with same error message
While this code works ok:
using Aspose.Words;
namespace ConsoleApplication1
{
class Program
{
static void Main(string[] args)
{
Document doc = new Document();
DocumentBuilder builder = new DocumentBuilder(doc);
builder.Font.Color = System.Drawing.Color.Blue;
builder.Write("aaa");
doc.Save("c:\\1.doc");
}
}
}
So it looks like COM Interop problem.
Answer: Please, check the answer provided here:
<http://www.aspose.com/community/forums/thread/240901/create-a-pivot-table-
from-multiple-data-ranges.aspx> I think, this approach should help you to
resolve the problem.
|
Python Access Parallel Port
Question: I've been trying to access the parallel port with pyParallel, which is in the
same sourceforge as PySerial:
<http://sourceforge.net/projects/pyserial/files/>
I'm getting a WidowsError: exception: priviledged instruciton. Has anyone used
this module before?
import parallel
p = parallel.Parallel()
Traceback (most recent call last):
File "<interactive input>", line 1, in <module>
File "C:\Python26\lib\site-packages\parallel\parallelwin32.py", line 74, in __init__
self.ctrlReg = _pyparallel.inp(self.ctrlRegAdr)
WindowsError: exception: priviledged instruction
Answer: Yep -- as I pondered in my comment, it's all about better sandboxing in
today's Windows versions -- there's a discussion [here](http://forums.bit-
tech.net/showthread.php?t=150570). There's also a possible solution
[here](http://logix4u.net/Legacy_Ports/Parallel_Port/Inpout32.dll_for_Windows_98/2000/NT/XP.html)
(at least up to XP, you'll need to try it if you have a newer Windows version)
with a Python example [here](http://logix4u.net/inpout32py.zip). I can't try
it out since I don't have any Windows around, but I hope it can help!
|
Printing python tkinter output
Question: I am trying to print the contents of a python tkinter canvas. I have tried
using the postscript method of canvas to create a postscript file, but I get a
blank page. I know this is because I have embedded widgets, and these do not
get rendered by the postscript method.
Before I rewrite my program to create a more printer-friendly layout, can
someone suggest a way to approach this problem? All of the programming books I
have ever read approach the problem of sending output to a printer with a bit
of hand-waving, something along the lines of: "It's a difficult problem that
depends on interacting with the operating system." I also have a hard time
finding resources about this because of all the pages related to printing to
the screen.
I am using Python 2.6, on Ubuntu 9.04.
Answer: Turns out that you have to update the canvas before exporting the postscript.
Like so:
from Tkinter import *
root = Tk()
canvas = Canvas(bg='white', width = 200, height = 200)
canvas.pack()
canvas.create_line(0, 0, 199, 199, fill="blue", width = 5)
canvas.create_line(0, 199, 199, 0, fill="blue", width = 5)
canvas.update()
canvas.postscript(file = "x.ps")
root.mainloop()
Thanks to Rio [here](http://www.python-
forum.org/pythonforum/viewtopic.php?f=15&t=12793#p59927) for the solution.
|
Problems trying to format currency with Python (Django)
Question: I have the following code in Django:
import locale
locale.setlocale( locale.LC_ALL, '' )
def format_currency(i):
return locale.currency(float(i), grouping=True)
It work on some computers in dev mode, but as soon as I try to deploy it on
production I get this error:
Exception Type: TemplateSyntaxError
Exception Value: Caught ValueError while rendering: Currency formatting is not possible using the 'C' locale.
Exception Location: /usr/lib/python2.6/locale.py in currency, line 240
The weird thing is that I can do this on the production server and it will
work without any errors:
python manage.py shell
>>> import locale
>>> locale.setlocale( locale.LC_ALL, '' )
'en_CA.UTF-8'
>>> locale.currency(1, grouping=True)
'$1.00'
I .. don't get it.i
Answer: On the production server, try
locale.setlocale( locale.LC_ALL, 'en_CA.UTF-8' )
instead of
locale.setlocale( locale.LC_ALL, '' )
When you use `''`, the locale is set to the user's default (usually specified
by the `LANG` environment variable). On the production server, that appears to
be 'C', while as a test user it appears to be 'en_CA.UTF-8'.
|
Python PEP8: Blank lines convention
Question: I am interested in knowing what is the Python convention for new lines between
the program? For example, consider this:
import os
def func1():
def func2():
What should be the ideal new line separation between:
1. the `import` modules and the functions?
2. the functions themselves?
I have read PEP8, but I wanted to confirm the above two points.
Answer: 1. two blank lines between the import statements and other code
2. two blank lines between each function
|
CherryPy configuration tools.staticdir.root problem
Question: How can I make my static-file root directories relative to my application root
folder (instead of a hard-coded path)?
In accordance with CP instructions
(http://www.cherrypy.org/wiki/StaticContent) I have tried the following in my
configuration file:
tree.cpapp = cherrypy.Application(cpapp.Root())
tools.staticdir.root = cpapp.current_dir
but when I run `cherrpy.quickstart(rootclass, script_name='/',
config=config_file)` I get the following error
_builtins.ValueError: ("Config error in section: 'global', option:
'tree.cpapp', value: 'cherrypy.Application(cpapp.Root())'. Config values must
be valid Python.", 'TypeError', ("unrepr could not resolve the name
'cpapp'",))_
I know I can do configuration from within the main.py file just before
quickstart is called (eg. using os.path.abspath(os.path.dirname(**file**))),
but I prefer using the idea of a separate configuration file if possible.
Any help would be appreciated (in case it is relevant, I am using CP 3.2 with
Python 3.1)
TIA Alan
Answer: When you refer to a module inside configuration entries, CherryPy first looks
for that module in `sys.modules`. So one solution would be to `import cpapp`
just before you call quickstart.
But if that lookup in `sys.modules` fails, CherryPy tries to `__import__` the
module. Since that is also failing, you might need to investigate whether your
`cpapp.py` module is indeed importable at all.
See the `lib/reprconf.py` module for all the gory details.
|
How to make item view render rich (html) text in PyQt?
Question: I'm trying to translate code from [this
thread](http://stackoverflow.com/questions/1956542/how-to-make-item-view-
render-rich-html-text-in-qt) in python:
import sys
from PyQt4.QtCore import *
from PyQt4.QtGui import *
__data__ = [
"Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.",
"Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat.",
"Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur.",
"Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum."
]
def get_html_box(text):
return '''<table border="0" width="100%"><tr width="100%" valign="top">
<td width="1%"><img src="softwarecenter.png"/></td>
<td><table border="0" width="100%" height="100%">
<tr><td><b><a href="http://www.google.com">titolo</a></b></td></tr>
<tr><td>{0}</td></tr><tr><td align="right">88/88/8888, 88:88</td></tr>
</table></td></tr></table>'''.format(text)
class HTMLDelegate(QStyledItemDelegate):
def paint(self, painter, option, index):
model = index.model()
record = model.listdata[index.row()]
doc = QTextDocument(self)
doc.setHtml(get_html_box(record))
doc.setTextWidth(option.rect.width())
painter.save()
ctx = QAbstractTextDocumentLayout.PaintContext()
ctx.clip = QRectF(0, option.rect.top(), option.rect.width(), option.rect.height())
dl = doc.documentLayout()
dl.draw(painter, ctx)
painter.restore()
def sizeHint(self, option, index):
model = index.model()
record = model.listdata[index.row()]
doc = QTextDocument(self)
doc.setHtml(get_html_box(record))
doc.setTextWidth(option.rect.width())
return QSize(doc.idealWidth(), doc.size().height())
class MyListModel(QAbstractListModel):
def __init__(self, parent=None, *args):
super(MyListModel, self).__init__(parent, *args)
self.listdata = __data__
def rowCount(self, parent=QModelIndex()):
return len(self.listdata)
def data(self, index, role=Qt.DisplayRole):
return index.isValid() and QVariant(self.listdata[index.row()]) or QVariant()
class MyWindow(QWidget):
def __init__(self, *args):
super(MyWindow, self).__init__(*args)
# listview
self.lv = QListView()
self.lv.setModel(MyListModel(self))
self.lv.setItemDelegate(HTMLDelegate(self))
self.lv.setResizeMode(QListView.Adjust)
# layout
layout = QVBoxLayout()
layout.addWidget(self.lv)
self.setLayout(layout)
if __name__ == "__main__":
app = QApplication(sys.argv)
w = MyWindow()
w.show()
sys.exit(app.exec_())
Element's size and position are not calculated correctly I guess, perhaps
because I haven't understand at all the style related parts from original
code. Can someone help me?
Answer: The code doesn't respect the desired target drawing area (`option.rect`):
ctx.clip = QRectF(0, option.rect.top(), option.rect.width(), option.rect.height())
The above clips the portion of the `QTextDocument` drawn to the specified
region. You really want to translate the painter so that the it starts
painting at the `topLeft()` of the rectangle and then extends for the
specified width and height. Since `documentLayout()` assumes the painter is at
the origin (i.e. in the position where it should draw), this is the fix:
def paint(self, painter, option, index):
model = index.model()
record = model.listdata[index.row()]
doc = QTextDocument(self)
doc.setHtml(get_html_box(record))
doc.setTextWidth(option.rect.width())
ctx = QAbstractTextDocumentLayout.PaintContext()
painter.save()
painter.translate(option.rect.topLeft());
painter.setClipRect(option.rect.translated(-option.rect.topLeft()))
dl = doc.documentLayout()
dl.draw(painter, ctx)
painter.restore()
|
Removing minimize/maximize buttons in Tkinter
Question: I have a python program which opens a new windows to display some 'about'
information. This window has its own close button, and I have made it non-
resizeable. However, the buttons to maximize and minimize it are still there,
and I want them gone.
I am using Tkinter, wrapping all the info to display in the Tk class.
The code so far is given below. I know its not pretty, and I plan on expanding
the info making it into a class, but I want to get this problem sorted before
moving along.
Anyone know how I can govern which of the default buttons are shown by the
windows manager?
def showAbout(self):
if self.aboutOpen==0:
self.about=Tk()
self.about.title("About "+ self.programName)
Label(self.about,text="%s: Version 1.0" % self.programName ,foreground='blue').pack()
Label(self.about,text="By Vidar").pack()
self.contact=Label(self.about,text="Contact: adress@gmail.com",font=("Helvetica", 10))
self.contact.pack()
self.closeButton=Button(self.about, text="Close", command = lambda: self.showAbout())
self.closeButton.pack()
self.about.geometry("%dx%d+%d+%d" % (175,\
95,\
self.myParent.winfo_rootx()+self.myParent.winfo_width()/2-75,\
self.myParent.winfo_rooty()+self.myParent.winfo_height()/2-35))
self.about.resizable(0,0)
self.aboutOpen=1
self.about.protocol("WM_DELETE_WINDOW", lambda: self.showAbout())
self.closeButton.focus_force()
self.contact.bind('<Leave>', self.contactMouseOver)
self.contact.bind('<Enter>', self.contactMouseOver)
self.contact.bind('<Button-1>', self.mailAuthor)
else:
self.about.destroy()
self.aboutOpen=0
def contactMouseOver(self,event):
if event.type==str(7):
self.contact.config(font=("Helvetica", 10, 'underline'))
elif event.type==str(8):
self.contact.config(font=("Helvetica", 10))
def mailAuthor(self,event):
import webbrowser
webbrowser.open('mailto:adress@gmail.com',new=1)
Answer: In general, what decorations the WM (window manager) decides to display can
not be easily dictated by a toolkit like Tkinter. So let me summarize what I
know plus what I found:
import Tkinter as tk
root= tk.Tk()
root.title("wm min/max")
# this removes the maximize button
root.resizable(0,0)
# # if on MS Windows, this might do the trick,
# # but I wouldn't know:
# root.attributes(toolwindow=1)
# # for no window manager decorations at all:
# root.overrideredirect(1)
# # useful for something like a splash screen
root.mainloop()
There is also the possibility that, for a `Toplevel` window other than the
root one, you can do:
toplevel.transient(1)
and this will remove the min/max buttons, but it also depends on the window
manager. From what I read, the MS Windows WM does remove them.
|
pythonic way to do something N times without an index variable?
Question: Every day I love python more and more.
Today, I was writing some code like:
for i in xrange(N):
do_something()
I had to do something N times. But each time didn't depend on the value of `i`
(index variable). I realized that I was creating a variable I never used
(`i`), and I thought "There surely is a more pythonic way of doing this
without the need for that useless index variable."
So... the question is: do you know how to do this simple task in a more
(pythonic) beautiful way?
Answer: A slightly faster approach than looping on `xrange(N)` is:
import itertools
for _ in itertools.repeat(None, N):
do_something()
|
Available disk space on an SMB share, via Python
Question: Does anyone know a way to get the amount of space available on a Windows
(Samba) share via Python 2.6 with its standard library? (also running on
Windows)
e.g.
>>> os.free_space("\\myshare\folder") # return free disk space, in bytes
1234567890
Answer: If [PyWin32](http://sourceforge.net/projects/pywin32/) is available:
free, total, totalfree = win32file.GetDiskFreeSpaceEx(r'\\server\share')
Where _free_ is a amount of free space available to the current user, and
_totalfree_ is amount of free space total. Relevant documentation: [PyWin32
docs](http://docs.activestate.com/activepython/2.4/pywin32/win32file__GetDiskFreeSpaceEx_meth.html),
[MSDN](http://msdn.microsoft.com/en-us/library/aa364937%28VS.85%29.aspx).
If PyWin32 is not guaranteed to be available, then for Python 2.5 and higher
there is [ctypes module](http://docs.python.org/library/ctypes.html) in
stdlib. Same function, using ctypes:
import sys
from ctypes import *
c_ulonglong_p = POINTER(c_ulonglong)
_GetDiskFreeSpace = windll.kernel32.GetDiskFreeSpaceExW
_GetDiskFreeSpace.argtypes = [c_wchar_p, c_ulonglong_p, c_ulonglong_p, c_ulonglong_p]
def GetDiskFreeSpace(path):
if not isinstance(path, unicode):
path = path.decode('mbcs') # this is windows only code
free, total, totalfree = c_ulonglong(0), c_ulonglong(0), c_ulonglong(0)
if not _GetDiskFreeSpace(path, pointer(free), pointer(total), pointer(totalfree)):
raise WindowsError
return free.value, total.value, totalfree.value
Could probably be done better but I'm not really familiar with ctypes.
|
Call another classes method in Python
Question: I'm tying to create a class that holds a reference to another classes method.
I want to be able to call the method. It is basically a way to do callbacks.
My code works until I try to access a class var. When I run the code below, I
get the error What am I doing wrong?
Brian
import logging
class yRunMethod(object):
"""
container that allows method to be called when method run is called
"""
def __init__(self, method, *args):
"""
init
"""
self.logger = logging.getLogger('yRunMethod')
self.logger.debug('method <%s> and args <%s>'%(method, args))
self.method = method
self.args = args
def run(self):
"""
runs the method
"""
self.logger.debug('running with <%s> and <%s>'%(self.method,self.args))
#if have args sent to function
if self.args:
self.method.im_func(self.method, *self.args)
else:
self.method.im_func(self.method)
if __name__ == "__main__":
import sys
#create test class
class testClass(object):
"""
test class
"""
def __init__(self):
"""
init
"""
self.var = 'some var'
def doSomthing(self):
"""
"""
print 'do somthing called'
print 'self.var <%s>'%self.var
#test yRunMethod
met1 = testClass().doSomthing
run1 = yRunMethod(met1)
run1.run()
Answer: I think you're making this **WAY** too hard on yourself (which is easy to do
;-). Methods of classes and instances are first-class objects in Python. You
can pass them around and call them like anything else. Digging into a method's
instance variables is something that should almost never be done. A simple
example to accomplish your goal is:
class Wrapper (object):
def __init__(self, meth, *args):
self.meth = meth
self.args = args
def runit(self):
self.meth(*self.args)
class Test (object):
def __init__(self, var):
self.var = var
def sayHello(self):
print "Hello! My name is: %s" % self.var
t = Test('FooBar')
w = Wrapper( t.sayHello )
w.runit()
|
I'm getting an error when trying to open a website url with Python 3.1, urllib & json: operation was attempted on something that is not a socket
Question: I'm getting an error when trying to open a website url with Python 3.1, urllib
& json
urllib.error.URLError:
Here's the code. The first website loads fine. The second one
import json
import urllib.request
import urllib.parse
import util
# This one works fine
response = urllib.request.urlopen('http://python.org/')
html = response.read()
print(html)
# parms - CSV filename, company, ....
p_filename = "c:\\temp\\test.csv"
jg_token = "zzzzzzzzzzzzzzzzzzzzzzzzz"
jg_proto = "https://"
jg_webst = "www.jigsaw.com/rest/"
jg_cmd_searchContact = "searchContact.json"
jg_key_companyName = "companyName"
jg_key_levels = "levels"
jg_key_departments = "departments"
jg_args = {
"token":jg_token,
jg_key_companyName: "Technical Innovations",
jg_key_departments: "HR"
}
jg_url = jg_proto + jg_webst + jg_cmd_searchContact + "?" + urllib.parse.urlencode(jg_args)
# This one generates teh error
result = json.load(urllib.request.urlopen(jg_url))
urllib.error.URLError:
File "c:\dev\xdev\PyJigsaw\searchContact.py", line 46, in result =
json.load(urllib.request.urlopen(jg_url))
File "c:\dev\tdev\Python31\Lib\urllib\request.py", line 121, in urlopen return
_opener.open(url, data, timeout)
File "c:\dev\tdev\Python31\Lib\urllib\request.py", line 349, in open response
= self._open(req, data)
File "c:\dev\tdev\Python31\Lib\urllib\request.py", line 367, in _open '_open',
req)
File "c:\dev\tdev\Python31\Lib\urllib\request.py", line 327, in _call_chain
result = func(*args)
File "c:\dev\tdev\Python31\Lib\urllib\request.py", line 1098, in https_open
return self.do_open(http.client.HTTPSConnection, req)
File "c:\dev\tdev\Python31\Lib\urllib\request.py", line 1075, in do_open raise
URLError(err)
Answer: Please edit the title and tags and maybe even the question body: This has
nothing to do with JSON and everything to do with Windows. It's also at a
lower level than urllib. (Probably in the SSL code.) Distilled:
Both of the following approaches fail on Python 3.1.2 for Vista, but work fine
on Linux (Python 3.1.3)
print( HTTPSConnection(hostname).request('GET',url).getresponse().read() )
print( urllib.request.urlopen('https://'+hostname+url).read() )
Change them to not use SSL, and then they work fine on Windows:
print( HTTPConnection(hostname).request('GET',url).getresponse().read() )
print( urllib.request.urlopen('http://'+hostname+url).read() )
|
how to pass an xml file to lxml to parse?
Question: I'm trying to parse an xml file using lxml. xml.etree allowed me to simply
pass the file name as a parameter to the `parse` function, so I attempted to
do the same with lxml.
My code:
from lxml import etree
from lxml import objectify
file = "C:\Projects\python\cb.xml"
tree = etree.parse(file)
but I get the error:
Traceback (most recent call last):
File "cb.py", line 5, in <module>
tree = etree.parse(file)
File "lxml.etree.pyx", line 2698, in lxml.etree.parse (src/lxml/lxml.etree.c:4
9590)
File "parser.pxi", line 1491, in lxml.etree._parseDocument (src/lxml/lxml.etre
e.c:71205)
File "parser.pxi", line 1520, in lxml.etree._parseDocumentFromURL (src/lxml/lx
ml.etree.c:71488)
File "parser.pxi", line 1420, in lxml.etree._parseDocFromFile (src/lxml/lxml.e
tree.c:70583)
File "parser.pxi", line 975, in lxml.etree._BaseParser._parseDocFromFile (src/
lxml/lxml.etree.c:67736)
File "parser.pxi", line 539, in lxml.etree._ParserContext._handleParseResultDo
c (src/lxml/lxml.etree.c:63820)
File "parser.pxi", line 625, in lxml.etree._handleParseResult (src/lxml/lxml.e
tree.c:64741)
File "parser.pxi", line 565, in lxml.etree._raiseParseError (src/lxml/lxml.etr
ee.c:64084)
lxml.etree.XMLSyntaxError: AttValue: " or ' expected, line 2, column 26
What am I doing wrong?
Answer: What you are doing wrong is (1) not checking whether you got the same outcome
by using `xml.etree` on the same file (2) not reading the error message, which
indicates a syntax error in line 2 of the file, way down stream from any file-
opening issue
|
Do you use Python mostly for its functional or object-oriented features?
Question: I see what seems like a majority of Python developers on StackOverflow
endorsing the use of concise functional tools like lambdas, maps, filters,
etc., while others say their code is clearer and more maintainable by not
using them. What is your preference?
Also, if you are a die-hard functional programmer or hardcore into OO, what
other specific programming practices do you use that you think are best for
your style?
Thanks in advance for your opinions!
Answer: I mostly use Python using object-oriented and procedural styles. Python is
actually not particularly well-suited to functional programming.
A lot of people think they are writing functional Python code by using lots of
`lambda`, `map`, `filter`, and `reduce`, but this is a bit over-simplified.
The hallmark feature of functional programming is a lack of state or side
effects. Important elements of a functional style are pure functions,
recursive algorithms, and first class functions.
Here are my thoughts on functional programming and Python:
* **Pure functions are great.** I do my best to make my module-level functions pure.
* Pure functions can be tested. Since they do not depend on outside state, they are much easier to test.
* Pure functions are able to support other optimizations, such as memoization and trivial parallelization.
* **Class-based programming can be pure.** If you want an equivalent to pure functions using Python classes (which is sometimes but not always what you want),
* Make your instances immutable. In particular, this mainly means to make your methods always return new instances of your class rather than changing the current one.
* Use dependency injection rather than getting stuff (like imported module) from global scope.
* This might not always be exactly what you want.
* **Don't try to avoid state all together.** This isn't a reasonable strategy in Python. For example, use `some_list.append(foo)` rather than `new_list = some_list + [foo]`, the former of which is more idiomatic and efficient. (Indeed, a ton of the "functional" solutions I see people use in Python are algorithmically suboptimal compared to just-as-simple or simpler solutions that are not functional or are just as functional but don't use the functional-looking tools.)
* Learn the best lessons from functional programming, for example **mutable state is dangerous.** Ask yourself, _Do I really want to change this X or do I want a new X?_
* One really common place this comes up is when processing a list. I would use
foo = [bar(item.baz()) for item in foo]
rather than
for index, _ in enumerate(foo):
foo[index] = bar(foo[index].baz())
and stuff like it. This avoids confusing bugs where the same list object is
stored elsewhere and shouldn't be changed. (If it _should_ be changed, then
there is a decent chance you have a design error. Mutating some list you have
referenced multiple places isn't a great way to share state.)
* **Don't use`map` and friends gratuitously.** There is nothing more functional about doing this.
* `map`/`filter` are **not** more functional than list comprehensions. List comprehensions were borrowed from Haskell, a pure functional language. `map` and especially `filter` can be harder to understand than a list comprehension. I would never use `map` or `filter` with a lambda but might if I had a function that already existed; I use `map` a decent bit.
* The same goes for `itertools.imap`/`ifilter` compared to generator expressions. (These things are somewhat lazy, which is something great we can borrow from the functional world.)
* Don't use `map` and `filter` for side effects. I see this with `map` a lot, which both makes hard-to-understand code, unneeded lists, and is decidedly not functional (despite people thinking it must be because of `map`.) Just use a for loop.
* `reduce` is confusing except for very simple cases. Python has for loops and there is no hurt in using them.
* **Don't use recursive algorithms.** This is one part of functional programming Python just does not support well. CPython (and I think all other Pythons) do not support tail call optimization. **Use iteration instead.**
* **Only use`lambda` when you are defining functions on the fly.** Anonymous functions aren't better than named functions, the latter of which are often more robust, maintainable, and documented.
|
python floating number
Question: i am kind of confused why python add some additional decimal number in this
case, please help to explain
>>> mylist = ["list item 1", 2, 3.14]
>>> print mylist ['list item 1', 2, 3.1400000000000001]
Answer: Floating point numbers are an approximation, they cannot store decimal numbers
exactly. Because they try to represent a very large range of numbers in only
64 bits, they must approximate to some extent.
It is very important to be aware of this, because it results in some weird
side-effects. For example, you might very reasonably think that the sum of ten
lots of `0.1` would be `1.0`. While this seems logical, it is also wrong when
it comes to floating point:
>>> f = 0.0
>>> for _ in range (10):
... f += 0.1
...
>>> print f == 1.0
False
>>> f
0.99999999999999989
>>> str(f)
1.0
You might think that `n / m * m == n`. Once again, floating-point world
disagrees:
>>> (1.0 / 103.0) * 103.0
0.99999999999999989
Or perhaps just as strangely, one might think that for all `n`, `n + 1 != n`.
In floating point land, numbers just don't work like this:
>>> 10.0**200
9.9999999999999997e+199
>>> 10.0**200 == 10.0**200 + 1
True
# How much do we have to add to 10.0**200 before its
# floating point representation changes?
>>> 10.0**200 == 10.0**200 + 10.0**183
True
>>> 10.0**200 == 10.0**200 + 10.0**184
False
See [What every computer scientist should know about floating point
numbers](http://docs.sun.com/source/806-3568/ncg_goldberg.html) for an
excellent summary of the issues.
If you need exact decimal representation, check out the
[decimal](http://docs.python.org/library/decimal.html) module, part of the
python standard library since 2.4. It allows you to specify the number of
significant figures. The downside is, it is much slower than floating point,
because floating point operations are implemented in hardware whereas decimal
operations happen purely in software. It also has its own imprecision issues,
but if you need exact representation of decimal numbers (e.g. for a financial
application) it's ideal.
For example:
>>> 3.14
3.1400000000000001
>>> import decimal
>>> decimal.Decimal('3.14')
>>> print decimal.Decimal('3.14')
3.14
# change the precision:
>>> decimal.getcontext().prec = 6
>>> decimal.Decimal(1) / decimal.Decimal(7)
Decimal('0.142857')
>>> decimal.getcontext().prec = 28
>>> decimal.Decimal(1) / decimal.Decimal(7)
Decimal('0.1428571428571428571428571429')
|
Use LaTeX Listings to correctly detect and syntax highlight embedded code of a different language in a script
Question: I have scripts that have one-liners or sort scripts from other languages
within them. How can I have LaTeX listings detect this and change the syntax
formating language within the script? This would be especially useful for awk
within bash I believe.
Bash
#!/bin/bash
echo "hello world"
R --vanilla << EOF
# Data on motor octane ratings for various gasoline blends
x <- c(88.5,87.7,83.4,86.7,87.5,91.5,88.6,100.3,
95.6,93.3,94.7,91.1,91.0,94.2,87.5,89.9,
88.3,87.6,84.3,86.7,88.2,90.8,88.3,98.8,
94.2,92.7,93.2,91.0,90.3,93.4,88.5,90.1,
89.2,88.3,85.3,87.9,88.6,90.9,89.0,96.1,
93.3,91.8,92.3,90.4,90.1,93.0,88.7,89.9,
89.8,89.6,87.4,88.9,91.2,89.3,94.4,92.7,
91.8,91.6,90.4,91.1,92.6,89.8,90.6,91.1,
90.4,89.3,89.7,90.3,91.6,90.5,93.7,92.7,
92.2,92.2,91.2,91.0,92.2,90.0,90.7)
x
length(x)
mean(x);var(x)
stem(x)
EOF
perl -n -e '
@t = split(/\t/);
%t2 = map { $_ => 1 } split(/,/,$t[1]);
$t[1] = join(",",keys %t2);
print join("\t",@t); ' knownGeneFromUCSC.txt
awk -F'\t' '{
n = split($2, t, ","); _2 = x
split(x, _) # use delete _ if supported
for (i = 0; ++i <= n;)
_[t[i]]++ || _2 = _2 ? _2 "," t[i] : t[i]
$2 = _2
}-3' OFS='\t' infile
Python
#!/usr/local/bin/python
print "Hello World"
os.system("""
VAR=even;
sed -i "s/$VAR/odd/" testfile;
for i in `cat testfile` ;
do echo $i; done;
echo "now the tr command is removing the vowels";
cat testfile |tr 'aeiou' ' '
""")
UPDATE: These are my current Listings settings in the preamble:
% This gives syntax highlighting in the python environment
\renewcommand{\lstlistlistingname}{Code Listings}
\renewcommand{\lstlistingname}{Code Listing}
\definecolor{gray}{gray}{0.5}
\definecolor{key}{rgb}{0,0.5,0}
\lstloadlanguages{Fortran,C++,C,[LaTeX]TeX,Python,bash,R, Perl}
\lstnewenvironment{python}[1][]{
\lstset{
language=python,
basicstyle=\ttfamily\small,
otherkeywords={1, 2, 3, 4, 5, 6, 7, 8 ,9 , 0, -, =, +, [, ], (, ), \{, \}, :, *, !},
keywordstyle=\color{blue},
stringstyle=\color{red},
showstringspaces=false,
emph={class, pass, in, for, while, if, is, elif, else, not, and, or,
def, print, exec, break, continue, return},
emphstyle=\color{black}\bfseries,
emph={[2]True, False, None, self},
emphstyle=[2]\color{key},
emph={[3]from, import, as},
emphstyle=[3]\color{blue},
upquote=true,
morecomment=[s]{"""}{"""},
commentstyle=\color{gray}\slshape,
rulesepcolor=\color{blue},#1
}
}{}
\lstnewenvironment{bash}{%
\lstset{%
language=bash,
otherkeywords={=, +, [, ], (, ), \{, \}, *},
% bash commands from:
%http://www.math.montana.edu/Rweb/Rhelp/00Index.html
emph={addgroup,adduser,alias,
ant,
apropos,apt-get,aptitude,aspell,awk,
basename,bash,bc,bg,break,builtin,bzip2,cal,case,cat,cd,cfdisk,chgrp,
chkconfig,chmod,chown,chroot,cksum,clear,cmp,comm,command,continue,
cp,cron,crontab,csplit,cut,date,dc,dd,ddrescue,declare,df,diff,diff3,
dig,dir,dircolors,dirname,dirs,dmesg,du,echo,egrep,eject,enable,env,
ethtool,eval,exec,exit,expand,expect,export,expr,false,fdformat,
fdisk,fg,fgrep,file,find,fmt,fold,for,format,free,fsck,ftp,function,
fuser,gawk,getopts,
git,
grep,groups,gzip,
gunzip,
,hash,head,help,history,hostname,
id,if,ifconfig,ifdown,ifup,import,install,
java, java6, java_cur
join,kill,killall,less,
let,ln,local,locate,logname,logout,look,lpc,lpr,lprint,lprintd,
lprintq,lprm,ls,lsof,make,man,mkdir,mkfifo,mkisofs,mknod,mmv,more,
mount,mtools,mtr,mv,
mysql,
netstat,nice,nl,nohup,notify-send,
noweb,noweave,
nslookup,op,
open,passwd,paste,pathchk,ping,pkill,popd,pr,printcap,printenv,
printf,ps,pushd,pwd,quota,quotacheck,quotactl,ram,rcp,read,
readarray,readonly,reboot,remsync,rename,renice,return,rev,rm,rmdir,
rsync,scp,screen,sdiff,sed,select,seq,set,sftp,shift,shopt,shutdown,
sleep,slocate,sort,source,split,ssh,strace,su,sudo,sum,
svn, svn2git,
symlink,sync,
tail,tar,tee,test,time,times,top,touch,tr,traceroute,trap,true,
tsort,tty,type,ulimit,umask,umount,unalias,uname,unexpand,uniq,
units,
unrar,
unset,unshar,until,useradd,usermod,users,uudecode,uuencode,
vdir,vi,vmstat,watch,wc,Wget,whereis,which,while,who,whoami,write,
zcat},
breaklines=true,
keywordstyle=\color{blue},
stringstyle=\color{red},
emphstyle=\color{black}\bfseries,
commentstyle=\color{gray}\slshape,
}
}{}
\lstnewenvironment{latexCode}[1]{\lstset{language=[latex]tex} \lstset{#1}}{}
\lstnewenvironment{Rcode}{
\lstset{%
language={R},
basicstyle=\small, % print whole listing small
keywordstyle=\color{black}, % style for keyword
% Function list from:
% http://www.math.montana.edu/Rweb/Rhelp/00Index.html
emph={abbreviate, abline,
abs, acos, acosh, all, all.names,
all.vars, anova, anova.glm, anova.lm, any,
aperm, append, apply, approx, approxfun,
apropos, Arg, args, Arithmetic, array,
arrows, as.array, as.call, as.character, as.complex,
as.data.frame, as.double, as.expression, as.factor, asin,
asinh, as.integer, as.list, as.logical, as.matrix,
as.na, as.name, as.null, as.numeric, as.ordered,
as.qr, as.real, assign, as.ts, as.vector,
atan, atan2, atanh, attach, attr,
attributes, autoload, .AutoloadEnv, axis, backsolve,
barplot, beta, binomial, box, boxplot,
boxplot.stats, break, browser, bw.bcv, bw.sj,
bw.ucv, bxp, c, .C, call,
cat, cbind, ceiling, character, charmatch,
chisq.test, chol, chol2inv, choose, class,
class<-, codes, coef, coefficients, coefficients.glm,
coefficients.lm, co.intervals, col, colnames, colors,
colours, Comparison, complete.cases, complex, Conj,
contour, contrasts, contr.helmert, contr.poly, contr.sum,
contr.treatment, convolve, cooks.distance, coplot, cor,
cos, cosh, count.fields, cov, covratio,
crossprod, cummax, cummin, cumprod, cumsum,
curve, cut, D, data, data.class,
data.entry, dataentry, data.frame, data.matrix, dbeta,
dbinom, dcauchy, dchisq, de, debug,
delay, demo, de.ncols, density, deparse,
de.restore, deriv, deriv.default, deriv.formula, de.setup,
detach, deviance, deviance.glm, deviance.lm, device,
Devices, dev.off, dexp, df, dfbetas,
dffits, df.residual, df.residual.glm, df.residual.lm, dgamma,
dgeom, dget, dhyper, diag, diff,
digamma, dim, dim<-, dimnames, dimnames<-,
dlnorm, dlogis, dnbinom, dnchisq, dnorm,
do.call, dotplot, double, dpois, dput,
drop, dt, dump, dunif, duplicated,
dweibull, dyn.load, edit, effects.glm, effects.lm,
eigen, else, emacs, end, environment,
environment<-, eval, exists, exp, expression,
Extract, factor, family, family.glm, fft,
finite, fitted, fitted.values, fitted.values.glm, fitted.values.lm,
fivenum, fix, floor, for, formals,
format, formatC, format.default, formula.default, formula.formula,
formula.terms, .Fortran, frame, frequency, function,
Gamma, gamma, gaussian, gc, gcinfo,
get, getenv, gl, glm, glm.control,
glm.fit, .GlobalEnv, graphics.off, gray, grep,
grid, gsub, hat, heat.colors, help,
hist, hsv, identify, if, ifelse,
Im, image, \%in\%, influence.measures, inherits,
integer, interactive, .Internal, inverse.gaussian, invisible,
invisible, IQR, is.array, is.atomic, is.call,
is.character, is.complex, is.data.frame, is.double, is.environment,
is.expression, is.factor, is.function, is.integer, is.language,
is.list, is.loaded, is.logical, is.matrix, is.na,
is.name, is.null, is.numeric, is.ordered, is.qr,
is.real, is.recursive, is.single, is.ts, is.unordered,
is.vector, lapply, lbeta, lchoose, legend,
length, LETTERS, letters, levels, levels<-,
lgamma, .lib.loc, .Library, library, library.dynam,
license, lines, lines.default, list, lm,
lm.fit, lm.influence, lm.wfit, load, locator,
log, log10, log2, Logic, logical,
lower.tri, lowess, ls, ls.diag, lsfit,
lsf.str, ls.print, ls.str, .Machine, Machine,
machine, macintosh, mad, match, match.arg,
match.call, matlines, mat.or.vec, matplot, matpoints,
matrix, max, mean, median, menu,
methods, min, missing, Mod, mode,
mode<-, model.frame, model.frame.default, model.matrix, model.matrix.default,
month.abb, month.name, mtext, mvfft, NA,
na.action, na.action.default, na.fail, names, na.omit,
nargs, nchar, NCOL, ncol, next,
NextMethod, nextn, nlevels, nlm, [.noquote,
noquote, NROW, nrow, NULL, numeric,
objects, on.exit, optimize, options, order,
ordered, outer, pairs, palette, par,
parse, paste, pbeta, pbinom, pcauchy,
pchisq, pentagamma, pexp, pf, pgamma,
pgeom, phyper, pi, pictex, piechart,
plnorm, plogis, plot, plot.default, plot.density,
plot.ts, plot.xy, pmatch, pmax, pmin,
pnbinom, pnchisq, pnorm, points, points.default,
poisson, polygon, polyroot, postscript, ppoints,
ppois, pretty, print, print.anova.glm, print.anova.lm,
print.data.frame, print.default, print.density, print.formula, print.glm,
print.lm, print.noquote, print.plot, print.summary.glm, print.summary.lm,
print.terms, print.ts, proc.time, prod, prompt,
prompt.default, prop.test, provide, .Provided, ps.options,
pt, punif, pweibull, q, qbeta,
qbinom, qcauchy, qchisq, qexp, qf,
qgamma, qgeom, qhyper, qlnorm, qlogis,
qnbinom, qnchisq, qnorm, qpois, qqline,
qqnorm, qqplot, qr, qr.coef, qr.fitted,
qr.Q, qr.qty, qr.qy, qr.R, qr.resid,
qr.solve, qr.X, qt, quantile, quasi,
quit, qunif, quote, qweibull, rainbow,
.Random.seed, range, rank, rbeta, rbind,
rbinom, rcauchy, rchisq, Re, readline,
read.table, real, rect, remove, rep,
repeat, replace, require, resid, residuals,
residuals.glm, residuals.lm, return, rev, rexp,
rf, rgamma, rgb, rgeom, rhyper,
RLIBS, rlnorm, rlogis, rm, rnbinom,
rnchisq, rnorm, round, row, row.names,
rownames, rpois, rstudent, rt, runif,
rweibull, sample, sapply, save, save.plot,
scale, scan, sd, segments, seq,
sequence, sign, signif, sin, sinh,
sink, solve, solve.qr, sort, source,
spline, splinefun, split, sqrt, start,
stem, stop, storage.mode, storage.mode<-, str,
str.data.frame, str.default, strheight, stripplot, strsplit,
structure, strwidth, sub, Subscript, substitute,
substr, substring, sum, summary, summary.glm,
summary.lm, svd, sweep, switch, symbol.C,
symbol.For, symnum, sys.call, sys.calls, sys.frame,
sys.frames, sys.function, sys.nframe, sys.on.exit, sys.parent,
sys.parents, system, system.date, system.time, t,
table, tabulate, tan, tanh, tapply,
tempfile, terms, terms.default, terms.formula, terms.terms,
terrain.colors, tetragamma, text, time, title,
topo.colors, trace, traceback, trigamma, trunc,
ts, tsp, t.test, typeof, unclass,
undebug, unique, uniroot, unlink, unlist,
untrace, update, update.formula, update.glm, update.lm,
upper.tri, UseMethod, var, vector, Version,
version, vi, warning, weighted.mean, weights.lm,
while, window, windows, write, x11,
xedit, xemacs, xinch, xor, xy.coords,
yinch}, % define a list of word to emphasis
stringstyle=\color{red},
emphstyle=\color{black}\bfseries, % define the way to emphase
showspaces=false, % show the space in code, or not
stringstyle=\ttfamily, % style of the string (like "hello word")
showstringspaces=false, % show the space in string, on not #1
commentstyle=\color{gray}\slshape,
tabsize=2, % sets default tabsize to 2 spaces
breaklines=true, % sets automatic line breaking
breakatwhitespace=false, % sets if automatic breaks should only happen at whitespace
}
}{}
\lstnewenvironment{Perl}{
\lstset{%
language={perl},
basicstyle=\small, % print whole listing small
keywordstyle=\color{black}, % style for keyword
emph={% From http://www.sdsc.edu/~moreland/courses/IntroPerl/docs/manual/pod/perlfunc.html
-X, run, abs, absolute, accept, accept, alarm, schedule, atan2,
arctangent, bind, binds, binmode, prepare, bless, create, caller,
get, chdir, change, chmod, changes, chomp, remove, chop, remove,
chown, change, chr, get, chroot, make, close, close, closedir, close,
connect, connect, continue, optional, cos, cosine, crypt, one-way,
dbmclose, breaks, dbmopen, create, defined, test, delete, deletes,
die, raise, do, turn, dump, create, each, retrieve, endgrent, be,
endhostent, be, endnetent, be, endprotoent, be, endpwent, be,
endservent, be, eof, test, eval, catch, exec, abandon, exists, test,
exit, terminate, exp, raise, fcntl, file, fileno, return, flock,
lock, fork, create, format, declare, formline, internal, getc, get,
getgrent, get, getgrgid, get, getgrnam, get, gethostbyaddr, get,
gethostbyname, get, gethostent, get, getlogin, return, getnetbyaddr,
get, getnetbyname, get, getnetent, get, getpeername, find, getpgrp,
get, getppid, get, getpriority, get, getprotobyname, get,
getprotobynumber, get, getprotoent, get, getpwent, get, getpwnam,
get, getpwuid, get, getservbyname, get, getservbyport, get,
getservent, get, getsockname, retrieve, getsockopt, get, glob,
expand, gmtime, convert, goto, create, grep, locate, hex, convert,
import, patch, int, get, ioctl, system-dependent, join, join, keys,
retrieve, kill, send, last, exit, lc, return, lcfirst, return,
length, return, link, create, listen, register, local, create,
localtime, convert, log, retrieve, lstat, stat, m//, match, map,
apply, mkdir, create, msgctl, SysV, msgget, get, msgrcv, receive,
msgsnd, send, my, declare, next, iterate, no, unimport, oct, convert,
open, open, opendir, open, ord, find, pack, convert, package,
declare, pipe, open, pop, remove, pos, find, print, output, printf,
output, prototype, get, push, append, q/STRING/, singly, qq/STRING/,
doubly, quotemeta, quote, qw/STRING/, quote, qx/STRING/, backquote,
rand, retrieve, read, fixed-length, readdir, get, readlink,
determine, recv, receive, redo, start, ref, find, rename, change,
require, load, reset, clear, return, get, reverse, flip, rewinddir,
reset, rindex, right-to-left, rmdir, remove, s///, replace, scalar,
force, seek, reposition, seekdir, reposition, select, reset, semctl,
SysV, semget, get, semop, SysV, send, send, setgrent, prepare,
sethostent, prepare, setnetent, prepare, setpgrp, set, setpriority,
set, setprotoent, prepare, setpwent, prepare, setservent, prepare,
setsockopt, set, shift, remove, shmctl, SysV, shmget, get, shmread,
read, shmwrite, write, shutdown, close, sin, return, sleep, block,
socket, create, socketpair, create, sort, sort, splice, add, split,
split, sprintf, formatted, sqrt, square, srand, seed, stat, get,
study, optimize, sub, declare, substr, get, symlink, create, syscall,
execute, sysread, fixed-length, system, run, syswrite, fixed-length,
tell, get, telldir, get, tie, bind, time, return, times, return,
tr///, transliterate, truncate, shorten, uc, return, ucfirst, return,
umask, set, undef, remove, unlink, remove, unpack, convert, unshift,
prepend, untie, break, use, load, utime, set, values, return, vec,
test, wait, wait, waitpid, wait, wantarray, get, warn, print, write,
print, y///, transliterate}, % define a list of word to emphasis
stringstyle=\color{red},
emphstyle=\color{black}\bfseries, % define the way to emphase
showspaces=false, % show the space in code, or not
stringstyle=\ttfamily, % style of the string (like "hello word")
showstringspaces=false, % show the space in string, on not #1
commentstyle=\color{gray}\slshape,
tabsize=2, % sets default tabsize to 2 spaces
breaklines=true, % sets automatic line breaking
breakatwhitespace=false, % sets if automatic breaks should only happen at whitespace
}
}{}
\lstnewenvironment{plaintext}{
\lstset{
tabsize=2, % sets default tabsize to 2 spaces
breaklines=true, % sets automatic line breaking
breakatwhitespace=false, % sets if automatic breaks should only happen at whitespace
basicstyle=\normalfont\ttfamily,
}
}{}
Answer: It is almost certainly easier to modify the Bash/Python highlighters than to
write a context-sensitive highlighter. I'm guessing that just adding the
keywords to the other highlighters should give acceptable results.
Modifying Pygments doesn't look too difficult, from Pygments' [Write your own
lexer](http://pygments.org/docs/lexerdevelopment/) documentation.
|
What is the difference between a module and a script in Python?
Question: Think the title summarizes the question :-)
Answer: A script is generally a directly executable piece of code, run by itself. A
module is generally a library, imported by other pieces of code.
Note that there's no internal distinction -- both are executable and
importable, although library code often won't do anything (or will just run
its unit tests) when executed directly and importing code designed to be a
script will cause it to execute, hence the common `if __name__ == "__main__"`
test.
|
Xml comparison in Python
Question: Building on [another SO
question](http://stackoverflow.com/questions/794331/xml-comparison-in-c), how
can one check whether two well-formed XML snippets are semantically equal. All
I need is "equal" or not, since I'm using this for unit tests.
In the system I want, these would be equal (note the order of 'start' and
'end'):
<?xml version='1.0' encoding='utf-8' standalone='yes'?>
<Stats start="1275955200" end="1276041599">
</Stats>
# Reordered start and end
<?xml version='1.0' encoding='utf-8' standalone='yes'?>
<Stats end="1276041599" start="1275955200" >
</Stats>
I have lmxl and other tools at my disposal, and a simple function that only
allows reordering of attributes would work fine as well!
* * *
Working snippet based on IanB's answer:
from formencode.doctest_xml_compare import xml_compare
# have to strip these or fromstring carps
xml1 = """ <?xml version='1.0' encoding='utf-8' standalone='yes'?>
<Stats start="1275955200" end="1276041599"></Stats>"""
xml2 = """ <?xml version='1.0' encoding='utf-8' standalone='yes'?>
<Stats end="1276041599" start="1275955200"></Stats>"""
xml3 = """ <?xml version='1.0' encoding='utf-8' standalone='yes'?>
<Stats start="1275955200"></Stats>"""
from lxml import etree
tree1 = etree.fromstring(xml1.strip())
tree2 = etree.fromstring(xml2.strip())
tree3 = etree.fromstring(xml3.strip())
import sys
reporter = lambda x: sys.stdout.write(x + "\n")
assert xml_compare(tree1,tree2,reporter)
assert xml_compare(tree1,tree3,reporter) is False
Answer: You can use
[formencode.doctest_xml_compare](http://bitbucket.org/ianb/formencode/src/tip/formencode/doctest_xml_compare.py#cl-70)
\-- the xml_compare function compares two ElementTree or lxml trees.
|
IDLE wont start Python 2.6.5
Question: I was using it as my primary text editor for quite sometime. However, one day
it just stopped working. This had happened to me several times before, so I
simply tried to end all procceses using windows task manager. However that
didn't work. I've recently tried getting it to work again. Whenever I try to
reopen it it informs me that it's subprocess couldn't connect. I tried
uninstalling it and reinstalling it, yet the problem persists.
Anyone have any other solutions?
Important facts: Windows 7, Python 2.6.5
Answer: Honestly I would advise you to stop using IDLE, the fact that it runs program
code in the same process as itself caused me a lot of problems when I used it,
including things like not refreshing imported modules that were modified.
Personally I switched to emacs, but you might like to try something like
Notepad++.
|
Counting the number of messages in an e-mail account with python
Question: is there any way, in Python, to have access to an e-mail account (I'll need
this for gmail but better if any works) and be able to see the number of
messages in the inbox (maybe even unread messages only)? Thank you.
Answer: **u Can Try This One**
import imaplib
obj = imaplib.IMAP4_SSL('imap.gmail.com', 993)
obj.login('username', 'password')
obj.select('Inbox') <\-- it will return total number of mail in Inbox i.e
('OK', ['50'])
obj.search(None,'UnSeen') <\-- it will return the list of uids for Unseen
mails
|
In Django : How to serialize dict object to json?
Question: I have this very basic problem,
>>> from django.core import serializers
>>> serializers.serialize("json", {'a':1})
Traceback (most recent call last):
File "<console>", line 1, in <module>
File "/usr/lib/pymodules/python2.6/django/core/serializers/__init__.py", line 87, in serialize
s.serialize(queryset, **options)
File "/usr/lib/pymodules/python2.6/django/core/serializers/base.py", line 40, in serialize
for field in obj._meta.local_fields:
AttributeError: 'str' object has no attribute '_meta'
>>>
How can this be done?
Answer: Also, since you seem to be using Python 2.6, you could just use the `json`
module directly:
import json
data = json.dumps({'a': 1})
|
Validating and filling default values in XML based on XSD in Python
Question: How do I fill the default value in my XML during validation against XSD? If my
attribute is not defined as `use="require"` and have `default="1"`, it could
be possible to fill these default values from the XSD to the XML.
Example: Original XML:
<a>
<b/>
<b c="2"/>
</a>
XSD scheme:
<xs:element name="a">
<xs:complexType>
<xs:sequence>
<xs:element name="b" maxOccurs="unbounded">
<xs:attribute name="c" default="1"/>
</xs:element>
</xs:sequence>
</xs:complexType>
</xs:element>
I want to validate the original XML using XSD and to fill all default values:
<a>
<b c="1"/>
<b c="2"/>
</a>
How do I get it in Python? With validation there is no problem (e.g.
XMLSchema). The problem are the default values.
Answer: To follow up on my comment, here's some code
from lxml import etree
from lxml.html import parse
schema_root = etree.XML('''\
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema">
<xs:element name="a">
<xs:complexType>
<xs:sequence>
<xs:element name="b" maxOccurs="unbounded">
<xs:complexType>
<xs:attribute name="c" default="1" type="xs:string"/>
</xs:complexType>
</xs:element>
</xs:sequence>
</xs:complexType>
</xs:element>
</xs:schema>''')
xmls = '''<a>
<b/>
<b c="2"/>
</a>'''
schema = etree.XMLSchema(schema_root)
parser = etree.XMLParser(schema = schema, attribute_defaults = True)
root = etree.fromstring(xmls, parser)
result = etree.tostring(root, pretty_print=True, method="xml")
print result
will give you
<a>
<b c="1"/>
<b c="2"/>
</a>
I've modified your XSD slightly, wrapped `xs:attribute` in `xs:complexType`
and added schema namespace. To have your defaults filled in, you need to pass
`attribute_defaults=True` to `etree.XMLParser()` and it should work.
|
2nd Year College - Learning - Microsoft Server Products
Question: As the title says, I just finished my first year of college (majoring in
Software Engineering). Fortunately my school likes Microsoft enough, and I can
get pretty much anything I want that Microsoft sells. I also can get IBM
Websphere and the like for free as well.
Earlier this year, I set up an oldish computer (2.6 Pentium D, x64) to run
ubuntu server headless. I'm predominately a Java developer, so Apache, Maven,
Nexus, Sonar, SVN, etc made it onto the machine. It worked really well for
personal and school projects, especially team projects (quick ramp up).
Anyways, I started to pick up C# to complement my Java knowledge (don't judge
me :P), and am interested in working with some of the associated Microsoft
equivalents.
The machine currently has the Ubuntu install, as well as Windows 7 Ultimate. I
do all of my actual development work off my laptop, also running Windows 7
Ultimate. I was wondering what software you would recommend putting on the
machine. I’m not actually serving anything off the machine itself, but in
Ubuntu I had it doing integration tests with Hudson on every commit, and
profiling my applications, etc, etc.
The machine would be running headless, and I would remote into it.
Here is what I am currently leaning towards / wondering about:
* Windows 7 Ultimate vs Windows Server 2008 (R2) (no one is really clear why I should go with one over the other)
* Windows Team Foundation
* Sharepoint (Never used it before, kind of meh about it)
* IBM Websphere or Glassfish (Some Java EE web server)
* SQL Server 2008
* A DVCS
In order to better control product conflicts / limit resource use, I’m
wondering if I should install things into virtual machines (I can get VmWare
or Microsoft Virtualization Products)
I also plan on installing everything I had running under Linux (it’s almost
entirely Java based development software, so it’ll run on both, only reason I
went with ubuntu during the year was because the apache build seemed better).
I’m primarily looking to become familiar with enterprise software development
tools, as well as get something functional that will help my development
process. (IE, I’ll still use project and assign tasks even though I might be
the only one to assign tasks to, just to practice doing so).
Is there any other software / configuration details I should explore? Opinions
on my current list? I primarily use C#, Java, and PHP. I'm familiar with ruby,
and python as well.
Thanks!
Answer: I can confirm that as long as you have the resources for VMs, then that is a
very smart way to go with installing many test environments, Windows does well
in these.
I want to tell you from personal experience, that Windows Server 2008 (and the
like) is a much better way to go than Windows 7/Vista. Microsoft puts a great
deal more efforts into building their server OS's than they do into the
client-side counterparts.
My experience goes as far back as alpha testing for Microsoft for Windows
Vista, and Server Longhorn. In every situation and setup I had/used/built,
Windows Server was always a more stable system. As for viruses, they don't
exist in Windows Server, they do however find themselves into relatively
clean/un used Vista/7 systems (not mine however).
I can give you many more reasons and examples from my experience if you like.
I would be happy to help, as security/stability is important and in my
business I put it first, and will gladly help someone else.
Use Windows Defender! its impressively successful in Windows Server, and use
freeware software such as spybot Search & Destroy for your Windows OS
protection.
As for coding, I highly recommend using Notepad++ as it has code coloring and
supports a huge assortment of coding languages. Great interface and awesome to
use.
...Feel free to ask for more. I specialize in Windows/Windows Server in my
business.
|
Python : get all exe files in current directory and run them?
Question: First of all this is not homework, I'm in a desperate need for a script that
will do the following, my problem is, I've never had to deal with python
before so I barely know how to use it - and I need it to launch unit tests in
TeamCity via a commandline build runner
What I need exactly is :
a *.bat file that will run the script
a python script that will :
* get all *_test.exe files in the current working directory
* run all the files which were the result of the search
Best regards
Answer:
import glob, os
def solution():
for fn in glob.glob("*_text.exe"):
os.startfile(fn)
|
Can Python ctypes load a 32bit C library on x86-64?
Question: I have a 64 bit RHEL host with 32 bit libraries installed. One vendor has a 32
bit .so I'd like to load into Python using ctypes.
from ctypes import CDLL
CDLL('32bitdinosaur.so')
OSError: 32bitdinosaur.so: wrong ELF class: ELFCLASS32
Of course 64 bit libraries are OK. Eg:
CDLL('libc.so.6')
Works fine.
Answer: It looks like the best way to do this is to have a 32 bit python in a separate
process load the .so, and call the 32 bit python from a 64 bit Python.
|
How exactly does a python (django) request happen? does it have to reparse all the codebase?
Question: With a scripting language like python (or php), things are not compiled down
to bytecode like in .net or java.
So does this mean that on every request, it has to go through the entire
application and parse/compile it? Or at least all the code required for the
given call stack?
Answer: > With a scripting language like python (or php), things are not compiled down
> to bytecode like in .net or java.
Wrong: everything you `import` in Python gets compiled to bytecode (and saved
as `.pyc` files if you can write to the directory containing the source you're
importing -- standard libraries &c are generally pre-compiled, depending on
the installation choices of course). Just keep the main script short and
simple (importing some module and calling a function in it) and you'll be
using compiled bytecode throughout. (Python's compiler is designed to be
extremely fast -- with implications including that it doesn't do a lot of
otherwise reasonable optimizations -- but avoiding it altogether is still
faster;-).
|
Python script to delete old SVN files lacks permission
Question: I'm trying to delete old SVN files from directory tree. `shutil.rmtree` and
`os.unlink` raise `WindowsError`s, because the script doesn't have permissions
to delete them. How can I get around that?
Here is the script:
# Delete all files of a certain type from a direcotry
import os
import shutil
dir = "c:\\"
verbosity = 0;
def printCleanMsg(dir_path):
if verbosity:
print "Cleaning %s\n" % dir_path
def cleandir(dir_path):
printCleanMsg(dir_path)
toDelete = []
dirwalk = os.walk(dir_path)
for root, dirs, files in dirwalk:
printCleanMsg(root)
toDelete.extend([root + os.sep + dir for dir in dirs if '.svn' == dir])
toDelete.extend([root + os.sep + file for file in files if 'svn' in file])
print "Items to be deleted:"
for candidate in toDelete:
print candidate
print "Delete all %d items? [y|n]" % len(toDelete)
choice = raw_input()
if choice == 'y':
deleted = 0
for filedir in toDelete:
if os.path.exists(filedir): # could have been deleted already by rmtree
try:
if os.path.isdir(filedir):
shutil.rmtree(filedir)
else:
os.unlink(filedir)
deleted += 1
except WindowsError:
print "WindowsError: Couldn't delete '%s'" % filedir
print "\nDeleted %d/%d files." % (deleted, len(toDelete))
exit()
if __name__ == "__main__":
cleandir(dir)
Not a single file is able to be deleted. What am I doing wrong?
Answer: Subversion usually makes all the `.svn` directories (and everything in them)
write protected. Probably you have to remove the write protection before you
can remove the files.
I'm not really sure how to do this best with Windows, but you should be able
to use
[`os.chmod()`](http://docs.python.org/library/os.html?highlight=chmod#os.chmod)
with the `stat.S_IWRITE` flag. Probably you have to iterate through all the
files in the `.svn` directories and make them all writable individually.
|
what is a fast way to output h5py dataset to text?
Question: I am using the h5py python package to read files in HDF5 format. (e.g.
somefile.h5) I would like to write the contents of a dataset to a text file.
For example, I would like to create a text file with the following contents:
1,20,31,75,142,324,78,12,3,90,8,21,1
I am able to access the dataset in python using this code:
import h5py
f = h5py.File('/Users/Me/Desktop/thefile.h5', 'r')
group = f['/level1/level2/level3']
dset = group['dsetname']
My naive approach is too slow, because my dataset has over 20000 entries:
# write all values to file
for index in range(len(dset)):
# do not add comma after last value
if index == len(dset)-1: txtfile.write(repr(dset[index]))
else: txtfile.write(repr(dset[index])+',')
txtfile.close()
return None
Is there a faster way to write this to a file? Perhaps I could convert the
dataset into a NumPy array or even a Python list, and then use some file-
writing tool?
(I could experiment with concatenating the values into a larger string before
writing to file, but I'm hoping there's something entirely more elegant)
Answer: Building a large string has the huge advantage of saving the need for the
goofy "last-time switch" thanks to the excellent `join` method of strings: to
replace your whole loop,
txtfile.write(','.join(repr(item) for item in dset))
I'm not sure how much more elegant you demand your code to be...;-)
|
Problem about python import with error
Question: I have write a small python module with one class and two functions. The
skeleton of the module is as following:
#file name: test_module.py
class TestClass:
@classmethod
def method1(cls, param1):
#to do something
pass
def __init__(self, param1):
#to do something
...
def fun1(*params):
#to do something
...
def fun2(*params):
#to do something
...
Another py file is a small script which imports function and class from the
module, as following:
import sys
from test_module import TestClass, fun1, fun2
def main(sys_argv):
li = range(5)
inst1 = TestClass(li)
fun1(inst1)
fun2(inst1)
return
if __name__ == "__main__":
main(sys.argv)
But when I execute the script, it is broken with following message:
* from: can't read /var/mail/test_module
* ./script.py: line 4: syntax error near unexpected token `('
* ./script.py: line 4: `def
main(sys_argv):'
I am not sure what the problem is. Is it a problem with import? But when I try
to import the module in ipython, everything is just ok.
Answer: Add a proper shebang line to your "small script". It's being interpreted as a
shell script.
|
PySerial and IronPython - get strange error
Question: I have a device connected to COM31. And the code that I need to create a
serial connection looks very simple
port = 31
trex_serial = serial.Serial(port - 1, baudrate=19200, stopbits=serial.STOPBITS_ONE, timeout=1)
The foollowing code works when I run it using Python2.6, but when executed by
IronPython2.6.1, this is what I get:
Traceback (most recent call last):
File "c:\Python26\lib\site-packages\serial\serialutil.py", line 188, in __init__
File "c:\Python26\lib\site-packages\serial\serialutil.py", line 236, in setPort
File "c:\Python26\lib\site-packages\serial\serialcli.py", line 139, in makeDeviceName
File "c:\Python26\lib\site-packages\serial\serialcli.py", line 17, in device
IndexError: index out of range: 30
I am not sure what is going on. PySerial clearly says that it is IronPython
compliant. Any ideas what am I doing wrong?
Answer: IronPython is asking .NET what the ports are. They are enumerated differently.
Most likely you are asking to open a connection that doesn't exist as far as
IronPython/.NET is concerned. To find out the "real" port number, use the
following code modified from the pySerial scan examples. Then use the number
next to the listed COM.
import serial
def scan():
#scan for available ports. return a list of tuples (num, name)
available = []
for i in range(256):
try:
s = serial.Serial(i)
available.append( (i, s.portstr))
s.close() # explicit close 'cause of delayed GC in java
except serial.SerialException:
pass
#You must add this check, otherwise the scan won't complete
except IndexError as Error:
pass
for n,s in available:
print "(%d) %s" % (n,s)
return available
The output looks like this for me:
(0) COM9
(1) COM15
(2) COM16
(3) COM1
(4) COM15
Then when you try to open the connection, use the number on the left NOT the
actual COMportNumber - 1. For instance I need to open a connection to COM15,
so using the above scan:
def IOCardConnect():
try:
connection = serial.Serial(4, 115200, timeout=1, parity=serial.PARITY_NONE)
print "Connection Succesful"
return connection
except serial.SerialException as Error:
print Error
Also, once you are connected, pySerial will expect bytes to write to the
connectio, not strings. So make sure you send like this:
#Use the built in bytes function to convert to a bytes array.
connection.write(bytes('Data_To_Send'))
|
create a class attribute without going through __setattr__
Question: What I have below is a class I made to easily store a bunch of data as
attributes. They wind up getting stored in a dictionary. I override
`__getattr__` and `__setattr__` to store and retrieve the values back in
different types of units. When I started overriding `__setattr__` I was having
trouble creating that initial dicionary in the 2nd line of `__init__` like
so...
`super(MyDataFile, self).__setattr__('_data', {})`
**My question...** Is there an easier way to create a class level attribute
with going through `__setattr__`? Also, should I be concerned about keeping a
separate dictionary or should I just store everything in `self.__dict__`?
#!/usr/bin/env python
from unitconverter import convert
import re
special_attribute_re = re.compile(r'(.+)__(.+)')
class MyDataFile(object):
def __init__(self, *args, **kwargs):
super(MyDataFile, self).__init__(*args, **kwargs)
super(MyDataFile, self).__setattr__('_data', {})
#
# For attribute type access
#
def __setattr__(self, name, value):
self._data[name] = value
def __getattr__(self, name):
if name in self._data:
return self._data[name]
match = special_attribute_re.match(name)
if match:
varname, units = match.groups()
if varname in self._data:
return self.getvaras(varname, units)
raise AttributeError
#
# other methods
#
def getvaras(self, name, units):
from_val, from_units = self._data[name]
if from_units == units:
return from_val
return convert(from_val, from_units, units), units
def __str__(self):
return str(self._data)
d = MyDataFile()
print d
# set like a dictionary or an attribute
d.XYZ = 12.34, 'in'
d.ABC = 76.54, 'ft'
# get it back like a dictionary or an attribute
print d.XYZ
print d.ABC
# get conversions using getvaras or using a specially formed attribute
print d.getvaras('ABC', 'cm')
print d.XYZ__mm
Answer: Your `__setattr__` in the example doesn't _do_ anything except put things in
`_data` instead of `__dict__` Remove it.
Change your `__getattr__` to use `__dict__`.
Store your value and units as a simple 2-tuple.
|
Python, dictionaries, and chi-square contingency table
Question: This is a problem I've been racking my brains on for a long time, so any help
would be great. I have a file which contains several lines in the following
format (word, time that the word occurred in, and frequency of documents
containing the given word within the given instance in time). Below is an
example of what the inputfile looks like.
#inputfile
<word, time, frequency>
apple, 1, 3
banana, 1, 2
apple, 2, 1
banana, 2, 4
orange, 3, 1
I have Python class below that I used to create 2-D dictionaries to store the
above file using as the key, and frequency as the value:
class Ddict(dict):
'''
2D dictionary class
'''
def __init__(self, default=None):
self.default = default
def __getitem__(self, key):
if not self.has_key(key):
self[key] = self.default()
return dict.__getitem__(self, key)
wordtime=Ddict(dict) # Store each inputfile entry with a <word,time> key
timeword=Ddict(dict) # Store each inputfile entry with a <time,word> key
# Loop over every line of the inputfile
for line in open('inputfile'):
word,time,count=line.split(',')
# If <word,time> already a key, increment count
try:
wordtime[word][time]+=count
# Otherwise, create the key
except KeyError:
wordtime[word][time]=count
# If <time,word> already a key, increment count
try:
timeword[time][word]+=count
# Otherwise, create the key
except KeyError:
timeword[time][word]=count
The question that I have pertains to calculating certain things while
iterating over the entries in this 2D dictionary. For each word 'w' at each
time 't', calculate:
1. The number of documents **with** word 'w' **within** time 't'. (a)
2. The number of documents **without** word 'w' **within** time 't'. (b)
3. The number of documents **with** word 'w' **outside** time 't'. (c)
4. The number of documents **without** word 'w' **outside** time 't'. (d)
Each of the items above represents one of the cells of a chi-square
contingency table for each word and time. Can all of these be calculated
within a single loop or do they need to be done one at a time?
Ideally, I would like the output to be what's below, where a,b,c,d are all the
items calculated above:
print "%s, %s, %s, %s" %(a,b,c,d)
In the case of the input file above, the result of trying to find the
contingency table for the word 'apple' at time '1' would be `(3,2,1,6)`. I'll
explain how each cell is calculated:
* '3' documents contain 'apple' within time '1'.
* There are '2' documents within time '1' that don't contain 'apple'.
* There is '1' document containing 'apple' outside time '1'.
* There are 6 documents outside time '1' that don't contain the word 'apple' (1+4+1).
Answer: Your 4 numbers for apple/1 add up to 12, more than the total number of
observations (11)! There are only 5 documents outside time '1' that don't
contain the word 'apple'.
You need to partition the observations into 4 disjoint subsets:
a: apple and 1 => 3
b: not-apple and 1 => 2
c: apple and not-1 => 1
d: not-apple and not-1 => 5
Here is some code that shows one way of doing it:
from collections import defaultdict
class Crosstab(object):
def __init__(self):
self.count = defaultdict(lambda: defaultdict(int))
self.row_tot = defaultdict(int)
self.col_tot = defaultdict(int)
self.grand_tot = 0
def add(self, r, c, n):
self.count[r][c] += n
self.row_tot[r] += n
self.col_tot[c] += n
self.grand_tot += n
def load_data(line_iterator, conv_funcs):
ct = Crosstab()
for line in line_iterator:
r, c, n = [func(s) for func, s in zip(conv_funcs, line.split(','))]
ct.add(r, c, n)
return ct
def display_all_2x2_tables(crosstab):
for rx in crosstab.row_tot:
for cx in crosstab.col_tot:
a = crosstab.count[rx][cx]
b = crosstab.col_tot[cx] - a
c = crosstab.row_tot[rx] - a
d = crosstab.grand_tot - a - b - c
assert all(x >= 0 for x in (a, b, c, d))
print ",".join(str(x) for x in (rx, cx, a, b, c, d))
if __name__ == "__main__":
# inputfile
# <word, time, frequency>
lines = """\
apple, 1, 3
banana, 1, 2
apple, 2, 1
banana, 2, 4
orange, 3, 1""".splitlines()
ct = load_data(lines, (str.strip, int, int))
display_all_2x2_tables(ct)
and here is the output:
orange,1,0,5,1,5
orange,2,0,5,1,5
orange,3,1,0,0,10
apple,1,3,2,1,5
apple,2,1,4,3,3
apple,3,0,1,4,6
banana,1,2,3,4,2
banana,2,4,1,2,4
banana,3,0,1,6,4
|
Sum of Digits, properties, hint please
Question: This is the problem:
> How many integers 0 ≤ n < 10^18 have the property that the sum of the digits
> of n equals the sum of digits of 137n?
This solution is grossly inefficient. What am I missing?
#!/usr/bin/env python
#coding: utf-8
import time
from timestrings import *
start = time.clock()
maxpower = 18
count = 0
for i in range(0, 10 ** maxpower - 1):
if i % 9 == 0:
result1 = list(str(i))
result2 = list(str(137 * i))
sum1 = 0
for j in result1:
sum1 += int(j)
sum2 = 0
for j in result2:
sum2 += int(j)
if sum1 == sum2:
print (i, sum1)
count += 1
finish = time.clock()
print ("Project Euler, Project 290")
print ()
print ("Answer:", count)
print ("Time:", stringifytime(finish - start))
Answer: You are trying to solve a Project Euler problem by brute force. That may work
for the first few problems, but for most problems you need think of a more
sophisticated approach.
Since it is IMHO not OK to give advice specific to this problem, take a look
at the general advice in [this
answer](http://stackoverflow.com/questions/1537306/recommended-reading-for-
solving-project-euler-problems/1537531#1537531).
|
Python Threading, loading one thread after another
Question: I'm working on a media player and am able to load in a single .wav and play
it. As seen in the code below.
foo = wx.FileDialog(self, message="Open a .wav file...", defaultDir=os.getcwd(), defaultFile="", style=wx.FD_MULTIPLE)
foo.ShowModal()
queue = foo.GetPaths()
self.playing_thread = threading.Thread(target=self.playFile, args=(queue[0], 'msg'))
self.playing_thread.start()
But the problem is, when I try to make the above code into a loop for multiple
.wav files. Such that while playing_thread.isActive == True, create and
.start() the thread. Then if .isActive == False, pop queue[0] and load the
next .wav file. Problem is, my UI will lock up and I'll have to terminate the
program. Any ideas would be appreciated.
Answer: Since is using wx.python, use a Delayedresult, look at wx demos for a complete
example.
Full minimal example:
import wx
import wx.lib.delayedresult as inbg
import time
class Player(wx.Frame):
def __init__(self):
self.titulo = "Music Player"
wx.Frame.__init__(self, None, -1, self.titulo,)
self.jobID = 0
self.Vb = wx.BoxSizer(wx.VERTICAL)
self.panel = wx.Panel(self,-1)
self.playlist = ['one','two']
self.abortEvent = inbg.AbortEvent()
self.msg = wx.StaticText(self.panel, -1, "...",pos=(30,-1))
self.msg.SetFont(wx.Font(9, wx.SWISS, wx.NORMAL, wx.BOLD))
self.action = wx.Button(self.panel, -1,"Play Playlist")
self.Bind(wx.EVT_BUTTON, self.StartPlaying,self.action)
self.Vb.Add(self.msg, 0, wx.EXPAND|wx.ALL, 3)
self.Vb.Add(self.action, 0, wx.EXPAND|wx.ALL, 3)
self.panel.SetSizer(self.Vb)
self.Show()
def StartPlaying(self,evt):
self.BgProcess(self.Playme)
def Playme(self,jobID, abortEvent):
print "in bg"
list = self.getPlayList()
print list
for music in list:
self.msg.SetLabel('Playing: %s' % music)
stop = 100
while stop > 0:
print stop
stop -=1
self.msg.SetLabel('Playing: %s [%s ]' % (music,stop))
def _resultConsumer(self, inbg):
jobID = inbg.getJobID()
try:
result = inbg.get()
return result
except Exception, exc:
return False
def getPlayList(self):
return self.playlist
def setPlayList(self,music):
self.playlist.appdend(music)
def BgProcess(self,executar):
self.abortEvent.clear()
self.jobID += 1
inbg.startWorker(self._resultConsumer, executar, wargs=(self.jobID,self.abortEvent), jobID=self.jobID)
app = wx.App(False)
demo = Player()
app.MainLoop()
|
How to call IronPython function from C#/F#?
Question: This is kind of follow up questions of
<http://stackoverflow.com/questions/2969194/integration-of-c-f-ironpython-and-
ironruby>
In order to use C/C++ function from Python, SWIG is the easiest solution. The
reverse way is also possible with Python C API, for example, if we have a
python function as follows
def add(x,y):
return (x + 10*y)
We can come up with the wrapper in C to use this python as follows.
double Add(double a, double b)
{
PyObject *X, *Y, *pValue, *pArgs;
double res;
pArgs = PyTuple_New(2);
X = Py_BuildValue("d", a);
Y = Py_BuildValue("d", b);
PyTuple_SetItem(pArgs, 0, X);
PyTuple_SetItem(pArgs, 1, Y);
pValue = PyEval_CallObject(pFunc, pArgs);
res = PyFloat_AsDouble(pValue);
Py_DECREF(X);
Py_DECREF(Y);
Py_DECREF(pArgs);
return res;
}
How about the IronPython/C# or even F#?
* How to call the C#/F# function from IronPython? Or, is there any SWIG equivalent tool in IronPython/C#?
* How to call the IronPython function from C#/F#? I guess I could use "engine.CreateScriptSourceFromString" or similar, but I need to find a way to call IronPython function look like a C#/F# function, not writing the code in a string, but reading from a file.
Answer: You say 'now writing the code in a string, but reading from a file', so ok,
read the file.
Python from F#:
let s = File.ReadAllLines("foo.py")
let engine = Python.CreateEngine()
let scriptSource =
engine.CreateScriptSourceFromString(s, SourceCodeKind.Statements)
...
F# from Python:
import clr
clr.AddReferenceToFile("SomeFsLib.dll")
I just got these from the links in this question. Have not tried it, but,
like, it's straightforward, I think it 'just works'. Dunno what else you are
asking for.
|
Convert a GTK python script to C
Question: The following script will take a screenshot on a Gnome desktop.
import gtk.gdk
w = gtk.gdk.get_default_root_window()
sz = w.get_size()
pb = gtk.gdk.Pixbuf(gtk.gdk.COLORSPACE_RGB,False, 8, sz[0], sz[1])
pb = pb.get_from_drawable(w, w.get_colormap(), 0, 0, 0, 0, sz[0], sz[1])
if (pb != None):
pb.save("screenshot.png", "png")
print "Screenshot saved to screenshot.png."
else:
print "Unable to get the screenshot."
Now, I've been trying to convert this to C and use it in one of the apps I am
writing but so far i've been unsuccessful. Is there any what to do this in C
(on Linux)?
Thanks! Jess.
Answer: I tested this and it does work, but there might be a simpler way to go from
GdkPixbuf to a png this was just the first one I found. (There's no
`gdk_pixbuf_save()`)
#include <unistd.h>
#include <stdio.h>
#include <gdk/gdk.h>
#include <cairo.h>
int main(int argc, char **argv)
{
gdk_init(&argc, &argv);
GdkWindow *w = gdk_get_default_root_window();
gint width, height;
gdk_drawable_get_size(GDK_DRAWABLE(w), &width, &height);
GdkPixbuf *pb = gdk_pixbuf_get_from_drawable(NULL,
GDK_DRAWABLE(w),
NULL,
0,0,0,0,width,height);
if(pb != NULL) {
cairo_surface_t *surf = cairo_image_surface_create(CAIRO_FORMAT_RGB24,
width, height);
cairo_t *cr = cairo_create(surf);
gdk_cairo_set_source_pixbuf(cr, pb, 0, 0);
cairo_paint(cr);
cairo_surface_write_to_png(surf, "screenshot.png");
g_print("Screenshot saved to screenshot.png.\n");
} else {
g_print("Unable to get the screenshot.\n");
}
return 0;
}
you'd compile like this: (assuming you save it as screenshot.c)
gcc -std=gnu99 `pkg-config --libs --cflags gdk-2.0` screenshot.c -o screenshot
Edit: the stuff to save the pixbuf could also look like: (note I didn't try
this out, but it's only one line...) Thanks to kaizer.se for pointing out my
fail at doc reading :P
gdk_pixbuf_save(pb, "screenshot.png", "png", NULL, NULL);
|
A simple Python extension in C
Question: I am trying to create a simple python extension module. I compiled the
following code into a transit.so dynamic module
#include <python2.6/Python.h>
static PyObject*
_print(PyObject* self, PyObject* args)
{
return Py_BuildValue("i", 10);
}
static PyMethodDef TransitMethods[] = {
{"print", _print, METH_VARARGS, ""},
{NULL, NULL, 0, NULL}
};
PyMODINIT_FUNC
inittransit(void)
{
Py_InitModule("transit", TransitMethods);
}
However, trying to call this from python
import transit
transit.print()
I obtain an error message
File "test.py", line 2
transit.print()
^
SyntaxError: invalid syntax
What's wrong with my code?
Answer: I'm guessing that it has to do with using a keyword as a function name. I
tried defining a function `print()` in a module just now for testing and got
the same sort of error. Try changing the name of this function slightly and
see if it fixes the problem.
|
How can I paste some string to the active window in Python?
Question: > **Possible Duplicate:**
> [How do I copy a string to the clipboard on Windows using
> Python?](http://stackoverflow.com/questions/579687/how-do-i-copy-a-string-
> to-the-clipboard-on-windows-using-python)
Can someone make me an example or explain to me how can I paste something to
the active window with Python?
Answer: It is easiest if you **use the[SendKeys](http://pypi.python.org/pypi/SendKeys)
package**. You can find a Windows installer for various Python versions
[here](http://www.rutherfurd.net/python/sendkeys/#dowloads).
The simplest use case, sending plain text, is very simple:
import SendKeys
SendKeys.SendKeys("Hello world")
You can do all sorts of nifty things **using key-codes to represent for
unprintable characters** :
import SendKeys
SendKeys.SendKeys("""
{LWIN}
{PAUSE .25}
r
Notepad.exe{ENTER}
{PAUSE 1}
Hello{SPACE}World!
{PAUSE 1}
%{F4}
n
""")
**Read[the documentation](http://www.rutherfurd.net/python/sendkeys/) for full
details.**
If for whatever reason you don't want to introduce a dependency on a non-
standard library package, you can [do the same
thing](http://code.activestate.com/recipes/65107-sendkeys-from-the-windows-
script-host-wsh-com/) using COM:
import win32api
import win32com.client
shell = win32com.client.Dispatch("WScript.Shell")
shell.Run("calc")
win32api.Sleep(100)
shell.AppActivate("Calculator")
win32api.Sleep(100)
shell.SendKeys("1{+}")
win32api.Sleep(500)
shell.SendKeys("2")
win32api.Sleep(500)
shell.SendKeys("~") # ~ is the same as {ENTER}
win32api.Sleep(500)
shell.SendKeys("*3")
win32api.Sleep(500)
shell.SendKeys("~")
win32api.Sleep(2500)
|
defining precision in python(2.6) division
Question:
from __future__ import division
To perform a division in which I need some percision. However, it gives a long
number, like:
1.876543820098765
I only need the the first two numbers after "." => 1.87 How can I do that?
Answer:
"%0.2f" % yournumber
As you said you don't want a rounded number, you might want to try
def twoDigits(x):
return int(100*x)/100.0
|
Terminate a python script from another python script
Question: I've got a long running python script that I want to be able to end from
another python script. Ideally what I'm looking for is some way of setting a
process ID to the first script and being able to see if it is running or not
via that ID from the second. Additionally, I'd like to be able to terminate
that long running process.
Any cool shortcuts exist to make this happen?
Also, I'm working in a Windows environment.
I just recently found an alternative answer here:
<http://stackoverflow.com/questions/788411/check-to-see-if-python-script-is-
running>
Answer: You could get your own PID (Process Identifier) through
import os
os.getpid()
and to kill a process in Unix
import os, signal
os.kill(5383, signal.SIGKILL)
to kill in Windows use
import subprocess as s
def killProcess(pid):
s.Popen('taskkill /F /PID {0}'.format(pid), shell=True)
You can send the PID to the other programm or you could search in the process-
list to find the name of the other script and kill it with the above script.
I hope that helps you.
|
MS SQL + Python (IronPython) timing out
Question: I'm querying MS SQL using python using the source code from
<http://www.ironpython.info/index.php/Accessing_SQL_Server>:
import clr
clr.AddReference('System.Data')
from System.Data import *
TheConnection = SqlClient.SqlConnection
("server=yourserver;database=News;uid=sa;password=password;timeout=0")
TheConnection.Open()
MyAction = SqlClient.SqlCommand("Select Headline from News", TheConnection)
MyReader = MyAction.ExecuteReader()
while MyReader.Read():
print MyReader[0]
MyReader.Close()
TheConnection.Close()
I just added `timeout=0`, but still I got :
EnvironmentError: System.Data.SqlClient.SqlException (0x80131904): Timeout
expired. The timeout period elapsed prior to completion of the operation
or the server is not responding.
I tried it with `timeout=1000000`, but still got the same error.
If I run the same SQL in the same machine using the MSSQL Client, it's totally
fine. Do you know how to avoid this timeout exception?
Answer: Try increasing the CommandTimeout property on the SqlCommand as described
here: <https://msdn.microsoft.com/en-
us/library/system.data.sqlclient.sqlcommand.commandtimeout(v=vs.110).aspx>
The timeout value in the connection string only controls the timeout for the
initial connection to the database. That will not help if your SQL query takes
a long time to execute so you need to use CommandTimeout instead.
|
How can I get href links from HTML using Python?
Question:
import urllib2
website = "WEBSITE"
openwebsite = urllib2.urlopen(website)
html = getwebsite.read()
print html
So far so good.
But I want only href links from the plain text HTML. How can I solve this
problem?
Answer: Try with [Beautifulsoup](http://www.crummy.com/software/BeautifulSoup/):
from BeautifulSoup import BeautifulSoup
import urllib2
import re
html_page = urllib2.urlopen("http://www.yourwebsite.com")
soup = BeautifulSoup(html_page)
for link in soup.findAll('a'):
print link.get('href')
In case you just want links starting with `http://`, you should use:
soup.findAll('a', attrs={'href': re.compile("^http://")})
|
akntextutils installation on mobile
Question: I tried to use akntextutils which ran successfully on emualator but trying to
run this on mobile device is a problem...
We using python 1.4.5 with a 2nd edition FP2 can u help us in this...
Answer: Traceback(most recent call last): File "", line 1, in? File
"c:\resource\site.py", line 109,in platsec_
import return imp.load_dynamic(name,name+'.pyd')
Symbian error:[errno-20] KErrCorrupt
this was the error when we placed the file in e:\sys\bin. at other places we
got no module named akntextutils kind of error.
ya, mobile is s60 ed2 fp2. nokia e63
|
How do you create a python package with a built in "test/main.py" main function?
Question: Desired directory tree:
Fibo
|-- src
| `-- Fibo.py
`-- test
`-- main.py
What I want is to call `python main.py` after cd'ing into test and executing
main.py will run all the unit tests for this package.
Currently if I do:
import Fibo
def main():
Fibo.fib(100)
if __name__ == "__main__":
main()
I get an error: "`ImportError: No module named Fibo`".
But if I do:
import sys
def main():
sys.path.append("/home/tsmith/svn/usefuldsp/trunk/Labs/Fibo/src")
import Fibo
Fibo.fib(100)
if __name__ == "__main__":
main()
This seems to fix my error. And I could move forward... but this isn't a
python package. This is more of a "collection of files" approach.
**How would you setup your testing to work in this directory structure?**
Answer: If I want to import a module that lives at a fixed, relative location to the
file I'm evaluating, I often do something like this:
try:
import Fibo
except ImportError:
import sys
from os.path import join, abspath, dirname
parentpath = abspath(join(dirname(__file__), '..'))
srcpath = join(parentpath, 'src')
sys.path.append(srcpath)
import Fibo
def main():
Fibo.fib(100)
if __name__ == "__main__":
main()
If you want to be a good namespace-citizen, you could `del` the no longer
needed symbols at the end of the `except` block.
|
Python not opening Japanese filenames
Question: I've been working on a python script to open up a file with a unicode name
(Japanese mostly) and save to a randomly generated (Non-unicode) filename in
Windows Vista 64-bit, and I'm having issues... It just doesn't work, it works
fine with non-unicode filenames (Even if it has unicode content), but the
second you try to pass a unicode filename in - it doesn't work.
Here's the code:
try:
import sys, os
inpath = sys.argv[1]
outpath = sys.argv[2]
filein = open(inpath, "rb")
contents = filein.read()
fileSave = open(outpath, "wb")
fileSave.write(contents)
fileSave.close()
testfile = open(outpath + '.test', 'wb')
testfile.write(inpath)
testfile.close()
except:
errlog = open('G:\\log.txt', 'w')
errlog.write(str(sys.exc_info()))
errlog.close()
And the error:
(<type 'exceptions.IOError'>, IOError(2, 'No such file or directory'), <traceback object at 0x01092A30>)
Answer: You have to convert your `inpath` to unicode, like this:
inpath = sys.argv[1]
inpath = inpath.decode("UTF-8")
filein = open(inpath, "rb")
I'm guessing you are using Python 2.6, because in Python 3, all strings are
unicode by default, so this problem wouldn't happen.
|
GUI tools and APIs for small/medium hierarchical data structures
Question: I'm trying to find a tool and library to edit, write and read data in a
hierarchical structure, similar to an LDAP tree, a Windows registry or a
Berkeley DB structure. The keys should represent some hierarchy, and the
values should have a relatively flexible format (typing is optional, but could
be useful). Here is an example:
Items/item_1/shape = "rectangle"
Items/item_1/top = 10
Items/item_1/left = 10
Items/item_1/width = 30
Items/item_1/height = 40
Items/item_2/shape = "square"
Items/item_2/top = 10
Items/item_2/left = 10
Items/item_2/width = 30
Items/item_3/shape = "circle"
Items/item_3/centre_x = 40
Items/item_3/centre_y = 50
Items/item_3/radius = 20
Items/item_3/colour = blue
The use-case would be:
1. Edit the data store via a convenient GUI. This could look like Windows Regedit or [Apache Directory Studio (LDAP Browser)](http://directory.apache.org/studio/screenshots.html).
2. Save that data into some store (e.g. a file).
3. Load this store from another application, which would be able to query it from an API. The library for this would ideally be callable from Python.
I'd like these operations to be reasonably fast for reading, but not have it
all loaded in memory in advance. The data store would be updated into the
application more or less manually, much less often than the data is read.
Being able to write to that data from the API would be a plus, but it's not a
strict requirement.
Queries would be good. For example (in pseudo query), "List Items/* where top
== 10" would return:
* Items/item_1
* Items/item_2
Ease of edition (via a good GUI) is one of the most important features.
I've considered a few options:
1. _An LDAP server_ answers most requirements (especially with the help of Apache Directory Studio). However, deploying an LDAP server just for that is too heavy. However good Apache Directory Studio is, the user still needs a reasonable understanding of LDAP (more than just explaining the tree hierachy). I'd also like some flexibility in the creation of schemas (or no schemas at all) rather than having to rely on an administrator to do this.
2. _Windows Regedit_. I'm not sure if it's possible, but I guess it's conceivable to have a registry-like file that has nothing to do with the actual windows registry, editable with custom content via Regedit. I would however like this GUI application to be available on non-Windows platforms and I'm not even sure there's a Python API to read a Windows registry file.
3. _RDF_. That could work. I'm sure there are fairly good Python libraries for semantic web. However, I don't need any reasoning capabilities. I'd rather have something fast and that doesn't use much memory. I'm not sure there are any good GUI tools to view and edit the tree (since it's geared towards webs and graphs).
There are certainly ways to build this sort of data structures on top of
existing systems like SQLite (for example), and this would be fine but I'm not
sure whether there's a good GUI that would come with it.
I'd appreciate comments and suggestions, thank you.
Answer: Forgive my densitosity, but if your hierarchy is anything but the roughest
kind of example, there must be hugely compelling, overpowering reasons for
your choosing that over, say, JSON or even (gulp!) XML:
<items>
<item>
<number>1</number>
<shape>rectangle</shape>
<top>10</top>
<left>10</left>
<width>30</width>
<height>40</height>
</item>
<item>
<number>2</number>
<shape>triangle</shape>
<top>20</top>
<left>50</left>
<width>30></width>
<height>40</height>
</item>
</items>
For XML, you know there are tons of editors that answer your needs. Same with
JSON. And I think there are also XML-> MySQL -> XML libraries.
Why not take that kind of approach?
|
issue while matching special char '\' in regular expression using '\\'
Question: I have very simple python script to match some special characters like -,+,-,.
But Im not getting expected result while using regex \ to match a single '\'
char.
import re
pat = r'[-+*\\]'
text = 'fdkjdfk\sdsdd'
if re.search(pat,text):
print re.search(pat,text).group()
else:
print "not found"
On running above code , it prints 'not found' It seems I am doing some mistake
here , any help appreciated !!!
Answer: `\` is an escape character.
Try escaping it:
text = 'fdkjdfk\\sdsdd'
|
Really simple way to deal with XML in Python?
Question: Musing over a [recently asked
question](http://stackoverflow.com/questions/3063319/), I started to wonder if
there is a _really simple_ way to deal with XML documents in Python. A
pythonic way, if you will.
Perhaps I can explain best if i give example: let's say the following - which
i think is a good example of how XML is (mis)used in web services - is the
response i get from http request to
<http://www.google.com/ig/api?weather=94043>
<xml_api_reply version="1">
<weather module_id="0" tab_id="0" mobile_row="0" mobile_zipped="1" row="0" section="0" >
<forecast_information>
<city data="Mountain View, CA"/>
<postal_code data="94043"/>
<latitude_e6 data=""/>
<longitude_e6 data=""/>
<forecast_date data="2010-06-23"/>
<current_date_time data="2010-06-24 00:02:54 +0000"/>
<unit_system data="US"/>
</forecast_information>
<current_conditions>
<condition data="Sunny"/>
<temp_f data="68"/>
<temp_c data="20"/>
<humidity data="Humidity: 61%"/>
<icon data="/ig/images/weather/sunny.gif"/>
<wind_condition data="Wind: NW at 19 mph"/>
</current_conditions>
...
<forecast_conditions>
<day_of_week data="Sat"/>
<low data="59"/>
<high data="75"/>
<icon data="/ig/images/weather/partly_cloudy.gif"/>
<condition data="Partly Cloudy"/>
</forecast_conditions>
</weather>
</xml_api_reply>
After loading/parsing such document, i would like to be able to access the
information as simple as say
>>> xml['xml_api_reply']['weather']['forecast_information']['city'].data
'Mountain View, CA'
or
>>> xml.xml_api_reply.weather.current_conditions.temp_f['data']
'68'
From what I saw so far, seems that `ElementTree` is the closest to what I
dream of. But it's not there, there is still some fumbling to do when
consuming XML. OTOH, what I am thinking is not that complicated - probably
just thin veneer on top of a parser - and yet it can decrease annoyance of
dealing with XML. Is there such a magic? (And if not - why?)
PS. Note I have tried `BeautifulSoup` already and while I like its approach,
it has real issues with empty `<element/>`s - see below in comments for
examples.
Answer: lxml has been mentioned. You might also check out
[lxml.objectify](http://codespeak.net/lxml/objectify.html) for some really
simple manipulation.
>>> from lxml import objectify
>>> tree = objectify.fromstring(your_xml)
>>> tree.weather.attrib["module_id"]
'0'
>>> tree.weather.forecast_information.city.attrib["data"]
'Mountain View, CA'
>>> tree.weather.forecast_information.postal_code.attrib["data"]
'94043'
|
In-place substitution of PyGTK widgets
Question: The code below creates a column of three labels. I would like to take the
middle label, and replace it with another widget using the text from the label
_after the initial creation of the UI_.
My actual use case is to take a GTKBuilder populated UI, and replace any
particular named label with a [dynamically wrapped
label](http://stackoverflow.com/questions/1893748/pygtk-dynamic-label-
wrapping) at run time. (I used a button here because it's simple but
distinct.) Then I can still use Glade to set up the UI, including the labels,
and not pepper my Python code with errant labels and strings if I later want
to make a label wrap.
The code as it stands does not work - the new button gets added to the end of
the column, and I want it to remain in the middle, where `label2` was to begin
with. What can I do, preferably in `wrap_in_button`, to make sure it ends up
in the correct place? I'd rather keep it general, since the parent may be a
`Box` or a `Table` or any general `Container`.
import pygtk
import gtk
def destroy(widget, data=None):
gtk.main_quit()
def wrap_in_button(label):
text = label.get_text()
button = gtk.Button(text)
parent = label.get_parent()
if parent:
parent.remove(label)
parent.add(button)
def Main():
# Pretend that this chunk is actually replaced by GTKBuilder work
# From here...
window = gtk.Window()
window.connect('destroy', destroy)
box = gtk.VBox()
window.add(box)
label1 = gtk.Label("Label 1")
label2 = gtk.Label("Label 2")
label3 = gtk.Label("Label 3")
box.pack_start(label1)
box.pack_start(label2)
box.pack_start(label3)
# ...up to here
# Comment this to see the original layout
wrap_in_button(label2)
window.show_all()
gtk.main()
if __name__ == "__main__":
Main()
Answer: I found the solution in the code of the _gazpacho_ interface designer.
You can use this function:
def replace_widget(current, new):
"""
Replace one widget with another.
'current' has to be inside a container (e.g. gtk.VBox).
"""
container = current.parent
assert container # is "current" inside a container widget?
# stolen from gazpacho code (widgets/base/base.py):
props = {}
for pspec in gtk.container_class_list_child_properties(container):
props[pspec.name] = container.child_get_property(current, pspec.name)
gtk.Container.remove(container, current)
container.add(new)
for name, value in props.items():
container.child_set_property(new, name, value)
The key seems to be to transfer the child properties from the old widget to
the new one after running `gtk.Container.add()`.
Applied to your example, this would be:
import pygtk
import gtk
def replace_widget(current, new):
"""
Replace one widget with another.
'current' has to be inside a container (e.g. gtk.VBox).
"""
container = current.parent
assert container # is "current" inside a container widget?
# stolen from gazpacho code (widgets/base/base.py):
props = {}
for pspec in gtk.container_class_list_child_properties(container):
props[pspec.name] = container.child_get_property(current, pspec.name)
gtk.Container.remove(container, current)
container.add(new)
for name, value in props.items():
container.child_set_property(new, name, value)
def destroy(widget, data=None):
gtk.main_quit()
def wrap_in_button(label):
text = label.get_text()
button = gtk.Button(text)
replace_widget(label, button)
def Main():
# Pretend that this chunk is actually replaced by GTKBuilder work
# From here...
window = gtk.Window()
window.connect('destroy', destroy)
box = gtk.VBox()
window.add(box)
label1 = gtk.Label("Label 1")
label2 = gtk.Label("Label 2")
label3 = gtk.Label("Label 3")
box.pack_start(label1)
box.pack_start(label2)
box.pack_start(label3)
# ...up to here
wrap_in_button(label2)
window.show_all()
gtk.main()
if __name__ == "__main__":
Main()
This works for me using Python 2.6.6 and PyGTK 2.17.
As a solution to your original problem, I used `label_set_autowrap()` [from
here](http://stackoverflow.com/questions/1893748/pygtk-dynamic-label-
wrapping/2016849#2016849) and it worked most of the time. However, it's not a
perfect solution as I wasn't able to correctly right-align auto-wrapped text.
|
Making Python sockets visible for outside world?
Question: i already have a post which is quite similiar, but i am getting more and more
frustrated because it seems nothing is wrong with my network setup. Other
software can be seen from the outside (netcat listen servers etc.) but not my
scripts.. How can this be?? Note: It works on LAN but not over the internet.
Server:
import socket
host = ''
port = 80001
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((host,port))
s.listen(1)
print 'Listening..'
conn, addr = s.accept()
print 'is up and running.'
print addr, 'connected.'
s.close()
print 'shut down.'
Client:
import socket
host = '80.xxx.xxx.xxx'
port = 80001
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((host,port))
s.close()
Somebody please help me.
Any help is greatly appreciated.
Jake
Answer: **Edited again to add:**
I think you may be missing some basics on socket communication. In order for
sockets to work, you need to ensure that the sockets on both your client and
server will meet. With your latest revision, your server is now bound to port
63001, but on the local loopback adapter: 127.0.0.1
Computers have multiple network adapters, at least 2: one is the local
loopback, which allows you to make network connections to the same machine in
a fast, performant manner (for testing, ipc etc), and a network adapter that
lets you connect to an actual network. Many computers may have many more
adapters (virtual adapters for vlans, wireless vs wired adapters etc), but
they will have at least 2.
So in your server application, you need to instruct it to bind the socket to
the proper network adapter.
host = ''
port = 63001
bind(host,port)
What this does in python is binds the socket to the loopback adapter (or
127.0.0.1/localhost).
In your client application you have:
host = '80.xxx.xxx.xxx'
port = 63001
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.connect((host,port))
Now what your client attempts to do is to connect to a socket to port 63001 on
80.xxx.xxx.xxx (which is your wireless internet adapter).
Since your server is listening on your loopback adapter, and your client is
trying to connect on your wireless adapter, it's failing, because the two ends
don't meet.
So you have two solutions here:
1. Change the client to connect to localhost by `host = 127.0.0.1`
2. Change the server to bind to your internet adapter by changing `host = 80.xxx.xxx.xxx`
Now the first solution, using localhost, will only work when your server and
client are on the same machine. Localhost always points back to itself (hence
loopback), no matter what machine you try. So if/when you decide to take your
client/server to the internet, you will have to bind to a network adapter that
is on the internet.
Edited to add:**
Okay with your latest revision it still won't work because `65535` is the
largest post available.
**Answer below was to the original revision of the question.**
In your code posted, you're listening (bound) on port `63001`, but your client
application is trying to connect to port `80`. Thats why your client can't
talk to your server. Your client needs to connect using port `63001` not port
`80`.
Also, unless you're running an HTTP server (or your python server will handle
HTTP requests), you really shouldn't bind to port `80`.
In your client code change:
import socket
host = '80.xxx.xxx.xxx'
port = 63001
And in your Server Code:
import socket
host = ''
port = 63001
s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
s.bind((socket.gethostbyname(socket.gethostname()), port ))
|
datetime issue with xlrd & xlwt python libs
Question: I'm trying to write some dates from one excel spreadsheet to another.
Currently, I'm getting a representation in excel that isn't quite what I want
such as this: "40299.2501157407"
I can get the date to print out fine to the console, however it doesn't seem
to work right writing to the excel spreadsheet -- the data must be a date type
in excel, I can't have a text version of it.
Here's the line that reads the date in:
date_ccr = xldate_as_tuple(sheet_ccr.cell(row_ccr_index, 9).value, book_ccr.datemode)
Here's the line that writes the date out:
row.set_cell_date(11, datetime(*date_ccr))
There isn't anything being done to date_ccr in between those two lines other
than a few comparisons.
Any ideas?
Answer: You can write the floating point number directly to the spreadsheet and set
the number format of the cell. Set the format using the `num_format_str` of an
`XFStyle` object when you write the value.
<https://secure.simplistix.co.uk/svn/xlwt/trunk/xlwt/doc/xlwt.html#xlwt.Worksheet.write-
method>
The following example writes the date 01-05-2010. (Also includes time of
06:00:10, but this is hidden by the format chosen in this example.)
import xlwt
# d can also be a datetime object
d = 40299.2501157407
wb = xlwt.Workbook()
sheet = wb.add_sheet('new')
style = xlwt.XFStyle()
style.num_format_str = 'DD-MM-YYYY'
sheet.write(5, 5, d, style)
wb.save('test_new.xls')
There are examples of number formats (num_formats.py) in the examples folder
of the xlwt source code. On my Windows machine: C:\Python26\Lib\site-
packages\xlwt\examples
You can read about how Excel stores dates (third section on this page):
<https://secure.simplistix.co.uk/svn/xlrd/trunk/xlrd/doc/xlrd.html>
|
How to create a parser which tokenizes a list of words taken from a file?
Question: I am trying to do a sintax text corrector for my compilers' class. The idea
is: I have some rules, which are inherent to the language (in my case,
Portuguese), like "A valid phrase is SUBJECT VERB ADJECTIVE", as in "Ruby is
great".
Ok, so first I have to tokenize the input "Ruby is great". So I have a text
file "verbs", with a lot of verbs, one by line. Then I have one text
"adjectives", one "pronouns", etc.
I am trying to use Ragel to create a parser, but I don't know how I could do
something like:
%%{
machine test;
subject = <open-the-subjects-file-and-accept-each-one-of-them>;
verb = <open-the-verbs-file-and-accept-each-one-of-them>;
adjective = <open-the-adjective-file-and-accept-each-one-of-them>;
main = subject verb adjective @ { print "Valid phrase!" } ;
}%%
I looked at ANTLR, Lex/Yacc, Ragel, etc. But couldn't find one that seemed to
solve this problem. The only way to do this that I could think of was to
preprocess Ragel's input file, so that my program reads the file and writes
its contents at the right place. But I don't like this solution either.
Does anyone knows how I could do this? There's no problem if it isn't with
Ragel, I just want to solve this problem. I would like to use Ruby or Python,
but that's not really necessary either.
Thanks.
Answer: If you want to read the files at compile time .. make them be of the format:
subject = \
ruby|\
python|\
c++
then use ragel's 'include' or 'import' statement (I forget which .. must check
the manual) to import it.
* * *
If you want to check the list of subjects at run time, maybe just make ragel
read 3 words, then have an action associated with each word. The action can
read the file and lookup if the word is good or not at runtime.
The action reads the text file and compares the word's contents.
%%{
machine test
action startWord {
lastWordStart = p;
}
action checkSubject {
word = input[lastWordStart:p+1]
for possible in open('subjects.txt'):
if possible == word:
fgoto verb
# If we get here do whatever ragel does to go to an error or just raise a python exception
raise Exception("Invalid subject '%s'" % word)
}
action checkVerb { .. exercise for reader .. ;) }
action checkAdjective { .. put adjective checking code here .. }
subject = ws*.(alnum*)>startWord%checkSubject
verb := : ws*.(alnum*)>startWord%checkVerb
adjective := ws*.)alnum*)>startWord%checkAdjective
main := subject;
}%%
|
howoto fix working directory is always home? (python)
Question: This is my first question.
My python script opens and reads from a present text file using the following
simple funct:
open("config.ini", "r")
As this is a relative path it is supposed to work because config.ini is placed
in the same directory like the script is when it is launched, that should be
the current working dir.
In fact this works perfectly on all of my 3 linux boxes, but I have one user
who demands support because he gets an error while opening config.ini. The
error raises because
os.path.exists("config.ini")
returns false even if the file is there!
Trying to fix this problem we found out that the only way to make it work is
to place config.ini in his home directory despite the supposed working
directory is another.
Also, if my script tries to create a file in the present working directory,
the file is always created in his home dir instead, and so I think that for
some reason his working dir is always home!
How can I troubleshoot this problem? Maybe I could introduce absolute paths,
but I am afraid that os.getcwd() would return the homedir instead of the
correct one.
Should I maybe suggest this user to fix his machine in some way?
Sorry for this long question but english is not my first language and I am a
beginner in coding, so have some difficulties to explain.
Thank you very much in advance! =)
Answer: Could it be that the user is executing your script _from_ his home directory?
I.e. suppose the script is in:
/home/user/test/foo/foo.py
But the user calls it thus:
/home/user> python test/foo/foo.py
In this case, the "current directory" the script sees is `/home/user`.
What you can do is find out the directory the script itself resides in by
calling this function:
import os
def script_dir():
return os.path.dirname(os.path.realpath(__file__))
It will always return the directory in which the script lives, not the current
directory which may be different. You can then store your configuration file
there safely.
|
Why can't I in python call HDIO_GETGEO?
Question:
#!/usr/bin/env python
# -*- coding: utf-8 -*-
########## THIS NOW WORKS! ##########
UNSUITABLE_ENVIRONMENT_ERROR = \
"This program requires at least Python 2.6 and Linux"
import sys
import struct
import os
from array import array
# +++ Check environment
try:
import platform # Introduced in Python 2.3
except ImportError:
print >>sys.stderr, UNSUITABLE_ENVIRONMENT_ERROR
if platform.system() != "Linux":
print >>sys.stderr, UNSUITABLE_ENVIRONMENT_ERROR
if platform.python_version_tuple()[:2] < (2, 6):
print >>sys.stderr, UNSUITABLE_ENVIRONMENT_ERROR
# --- Check environment
HDIO_GETGEO = 0x301 # Linux
import fcntl
def get_disk_geometry(fd):
geometry = array('c',"XXXXXXXX")
fcntl.ioctl(fd, HDIO_GETGEO, geometry, True)
heads, sectors, cylinders, start = \
struct.unpack("BBHL",geometry.tostring())
return { 'heads' : heads, 'cylinders': cylinders, 'sectors': sectors, "start": start }
from pprint import pprint
fd=os.open("/dev/sdb", os.O_RDWR)
pprint(get_disk_geometry(fd))
Answer: Nobody seems to be able to tell me why you can't do this, but you can do it
with ctypes so it doesn't really matter.
#!/usr/bin/env python
from ctypes import *
import os
from pprint import pprint
libc = CDLL("libc.so.6")
HDIO_GETGEO = 0x301 # Linux
class HDGeometry(Structure):
_fields_ = (("heads", c_ubyte),
("sectors", c_ubyte),
("cylinders", c_ushort),
("start", c_ulong))
def __repr__(self):
return """Heads: %s, Sectors %s, Cylinders %s, Start %s""" % (
self.heads, self.sectors, self.cylinders, self.start)
def get_disk_geometry(fd):
""" Returns the heads, sectors, cylinders and start of disk as rerpoted by
BIOS. These us usually bogus, but we still need them"""
buffer = create_string_buffer(sizeof(HDGeometry))
g = cast(buffer, POINTER(HDGeometry))
result = libc.ioctl(fd, HDIO_GETGEO, byref(buffer))
assert result == 0
return g.contents
if __name__ == "__main__":
fd = os.open("/dev/sdb", os.O_RDWR)
print repr(get_disk_geometry(fd))
|
how to integrate spiders and scrapy-ctl.py
Question: I am new to python and scrapy and hence am getting some basic doubts(please
spare my ignorance about some fundamentals,which i m willing to learn :D).
Right now I am writing some spiders and implementing them using scrapy-ctl.py
from the command line by typing:
C:\Python26\dmoz>python scrapy-ctl.py crawl spider
But I do not want two separate python codes and a command line to implement
this.I want to somehow define a spider and make it crawl urls by writing and
running a single python code.I could notice that in the file scrapy-ctl.py,
'execute' of type _function_ is imported,but i am clueless as to how this
function can be defined in the code containing spider.Could someone explain me
how to do this, if it is possible because it greatly reduces the work.
Thanks in advance!!
Answer: > But I do not want two separate python codes and a command line to implement
> this. I want to somehow define a spider and make it crawl urls by writing
> and running a single python code.
I'm not sure the effort pays out, if you just want to scrape something. You
have at least two options:
* Dig into `scrapy/cmdline.py`. You'll see that this is a kind of dispatch script, finally handing over the work to the `run` method for the specified command, here `crawl` (in `scrapy/commands/crawl.py`). Look at line 54, I think `scrapymanager.start()` will begin your actual command, after some setup.
* A little hacky method: use pythons [`subprocess`](http://docs.python.org/library/subprocess.html) module to have one your project and execution in one file (or project).
|
Python Google App Engine: Call specific method from yaml file?
Question: I am new to database programming with Google App Engine and am programming in
Python. I was wondering if I am allowed to have one Python file with several
request handler classes, each of which has get and post methods. I know that
the yaml file allows me to specify which scripts are run with specific urls,
like the example below:
handlers:
- url: /.*
script: helloworld.py
How would I tell it to run a specific method that is in one of the classes in
the .py file? Is that even possible/allowed? Do I need to separate the
different request handler classes into different python files? My
understanding of databases is rather shallow at the moment, so I could be
making no sense.
Thanks.
Answer: > I was wondering if I am allowed to have one Python file with several request
> handler classes, each of which has get and post methods.
Sure! That `app.yaml` just transfers control to `helloworld.py`, which will
run the `main` function defined in that file -- and that function typically
sets up a WSGI app which dispatches appropriately, depending on the URL, to
the right handler class. For example, look at the sample code
[here](http://code.google.com/appengine/docs/python/gettingstarted/handlingforms.html),
very early on in the tutorial:
application = webapp.WSGIApplication(
[('/', MainPage),
('/sign', Guestbook)],
debug=True)
def main():
run_wsgi_app(application)
if __name__ == "__main__":
main()
I'm not copying the `import` statements and class definitions, because they
don't matter: this is an example of how a single `.py` file dispatches to
various handler classes (two in this case).
This doesn't mean the yaml file lets you call any method whatsoever, of
course: rather, it hands control to a `.py` file, whose `main` is responsible
for all that follows (and e.g. with the `webapp` mini-framework that comes
with App Engine, it will always be `get` or `post` method [[or `put`,
`delete`, ..., etc, if you also support those -- few do unless they're being
especially RESTful;-)]] being called depending on the exact HTTP method and
URL in the incoming request.
|
Shutting down gracefully from ThreadingTCPServer
Question: I've created a simple test app (Python 2.6.1) that runs a ThreadingTCPServer,
based on the example [here](http://danieldandrada.blogspot.com/2007/09/python-
socketserverthreadingtcpserver.html). If the client sends a command "bye" I
want to shut down the server and exit cleanly from the application. The exit
part works OK, but when I try to re-run the app, I get:
socket.error: [Errno 48] Address already in use
I tried the solution given
[here](http://stackoverflow.com/questions/2274320/socketserver-
threadingtcpserver-cannot-bind-to-address-after-program-restart) for setting
the socket options but that didn't seem to help. I've tried various ways to
close the server down, but always get the same error.
Any idea what I'm doing wrong?
import SocketServer
import socket
import sys
import threading
import time
class RequestHandler(SocketServer.BaseRequestHandler):
def setup(self):
print("Connection received from %s" % str(self.client_address))
self.request.send("Welcome!\n")
def handle(self):
while 1:
data = self.request.recv(1024)
if (data.strip() == 'bye'):
print("Leaving server.")
self.finish()
self.server.shutdown()
# None of these things seem to work either
#time.sleep(2)
#del self.server.socket
#self.server.socket.shutdown(socket.SHUT_WR)
#self.server.socket.close()
#self.server.server_close()
break
def finish(self):
self.request.send("Goodbye! Please come back soon.")
if __name__ == "__main__":
server = SocketServer.ThreadingTCPServer(("localhost", 9999), RequestHandler)
# This doesn't seem to help.
#server.socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEPORT, 1)
#server.socket.setsockopt(socket.SOL_SOCKET, socket.SO_REUSEADDR, 1)
server.serve_forever()
print("Exiting program.")
Answer: If you have not already found an answer, I believe this may assist...
[How to close a socket left open by a killed
program?](http://stackoverflow.com/questions/5875177/how-to-close-a-socket-
left-open-by-a-killed-program/5875178#5875178)
However, this is the same solution offered by Alex, so perhaps this is just an
opportunity to close an old question.
|
Converting from utf-16 to utf-8 in Python 3
Question: I'm programming in Python 3 and I'm having a small problem which I can't find
any reference to it on the net.
As far as I understand the default string in is utf-16, but I must work with
utf-8, I can't find the command that will convert from the default one to
utf-8. I'd appreciate your help very much.
Answer: In Python 3 there are two different datatypes important when you are working
with string manipulation. First there is the string class, an object that
represents unicode code points. Important to get is that this string is not
some bytes, but really a sequence of characters. Secondly, there is the bytes
class, which is just a sequence of bytes, often representing an string stored
in an encoding (like utf-8 or iso-8859-15).
What does this mean for you? As far as I understand you want to read and write
utf-8 files. Let's make a program that replaces all 'ć' with 'ç' characters
def main():
# Let's first open an output file. See how we give an encoding to let python know, that when we print something to the file, it should be encoded as utf-8
with open('output_file', 'w', encoding='utf-8') as out_file:
# read every line. We give open() the encoding so it will return a Unicode string.
for line in open('input_file', encoding='utf-8'):
#Replace the characters we want. When you define a string in python it also is automatically a unicode string. No worries about encoding there. Because we opened the file with the utf-8 encoding, the print statement will encode the whole string to utf-8.
print(line.replace('ć', 'ç'), out_file)
So when should you use bytes? Not often. An example I could think of would be
when you read something from a socket. If you have this in an bytes object,
you could make it a unicode string by doing bytes.decode('encoding') and visa
versa with str.encode('encoding'). But as said, probably you won't need it.
Still, because it is interesting, here the hard way, where you encode
everything yourself:
def main():
# Open the file in binary mode. So we are going to write bytes to it instead of strings
with open('output_file', 'wb') as out_file:
# read every line. Again, we open it binary, so we get bytes
for line_bytes in open('input_file', 'rb'):
#Convert the bytes to a string
line_string = bytes.decode('utf-8')
#Replace the characters we want.
line_string = line_string.replace('ć', 'ç')
#Make a bytes to print
out_bytes = line_string.encode('utf-8')
#Print the bytes
print(out_bytes, out_file)
Good reading about this topic (string encodings) is
<http://www.joelonsoftware.com/articles/Unicode.html>. Really recommended
read!
Source: <http://docs.python.org/release/3.0.1/whatsnew/3.0.html#text-vs-data-
instead-of-unicode-vs-8-bit>
(P.S. As you see, I didn't mention utf-16 in this post. I actually don't know
whether python uses this as internal decoding or not, but it is totally
irrelevant. At the moment you are working with a string, you work with
characters (code points), not bytes.
|
associative list python
Question: i am parsing some html form with Beautiful soup. Basically i´ve around 60
input fields mostly radio buttons and checkboxes. So far this works with the
following code:
from BeautifulSoup import BeautifulSoup
x = open('myfile.html','r').read()
out = open('outfile.csv','w')
soup = BeautifulSoup(x)
values = soup.findAll('input',checked="checked")
# echoes some output like ('name',1) and ('value',4)
for cell in values:
# the following line is my problem!
statement = cell.attrs[0][1] + ';' + cell.attrs[1][1] + ';\r'
out.write(statement)
out.close()
x.close()
As indicating in the code my problem ist where the attributes are selected,
because the HTML template is ugly, mixing up the sequence of arguments that
belong to a input field. I am interested in name="somenumber"
value="someothernumber" . Unfortunately my attrs[1] approach does not work,
since name and value do not occur in the same sequence in my html.
Is there any way to access the resulting BeautifulSoup list associatively?
Thx in advance for any suggestions!
Answer: I'm fairly sure you can use the attribute name like a key for a hash:
print cell['name']
|
How to get Field names from a SQL database into a list in python
Question: Here is a the code I have so far:
from ConfigParser import *
import MySQLdb
configuration = ConfigParser()
configuration.read('someconfigfile.conf')
db = MySQLdb.connect(
host = configuration.get('DATABASE', 'MYSQL_HOST'),
user = configuration.get('DATABASE', 'MYSQL_USER'),
passwd = configuration.get('DATABASE', 'MYSQL_PASS'),
db = configuration.get('DATABASE', 'MYSQL_DB'),
port = configuration.getint('DATABASE', 'MYSQL_PORT'),
ssl = {
'ca': configuration.get('SSL_SETTINGS', 'SSL_CA'),
'cert': configuration.get('SSL_SETTINGS', 'SSL_CERT'),
'key': configuration.get('SSL_SETTINGS', 'SSL_KEY')
},
)
cursor = db.cursor()
sql = "SELECT column_name FROM information_schema.columns WHERE table_name='met';"
cursor.execute(sql)
list = cursor.fetchall()
print list
this is what prints:
(('field',), ('field',), ('field',), ('field',), ('field',), ('field',), ('field',), ('field',), ('field',), ('field',), ('field',), ('field',), ('field',), ('field',), ('pk_wind_spd2',), ('field',))
And I am getting a tuple instead of a list. I would prefer to have a list of
strings
Answer: Don't shadow built-ins (list), change to
`alist = cursor.fetchall()`
This generator expression will get you the column names in a tuple:
`tuple(i[0] for i in alist)`
|
python: validate kerberos ticket
Question: I'm wondering - if anyone has an elegant solution to checking for a valid
Kerberos ticket using Python. I'm not seeing anyway with `kinit` or `klist`
that will show if a ticket is expired with a return code but I could run
`klist` and use a regex for the output .
Answer: You've got two options: the first is to use 'klist -s' and check the return
code. The nicer option is to use the [python-
krbV](https://pypi.python.org/pypi/python-krbV) module:
import krbV
def has_ticket():
'''
Checks to see if the user has a valid ticket.
'''
ctx = krbV.default_context()
cc = ctx.default_ccache()
try:
princ = cc.principal()
retval = True
except krbV.Krb5Error:
retval = False
return retval
|
error in connecting to a smtp server with python
Question: import smtplib
SERVER = "my.smtp.server.com"
FROM = "myemail@somehost.ca" TO = ["someemail@somehost.mun.ca"] # must be a
list
SUBJECT = "Hello!"
TEXT = "hello"
Here is my code:
# Prepare actual message
message = """\
From: %s
To: %s
Subject: %s
%s
""" % (FROM, ", ".join(TO), SUBJECT, TEXT)
# Send the mail
server = smtplib.SMTP(SERVER)
server.login('loginname','password')
and this is the error I get:
Traceback (most recent call last):
File "C:\Documents and Settings\Desktop\New Text Document.py", line 24, in ?
server = smtplib.SMTP(SERVER)
File "C:\Python24\lib\smtplib.py", line 241, in __init__
(code, msg) = self.connect(host, port)
File "C:\Python24\lib\smtplib.py", line 289, in connect
for res in socket.getaddrinfo(host, port, 0, socket.SOCK_STREAM):
gaierror: (11001, 'getaddrinfo failed')
what do I do next?
Answer: There is no ip for `my.smtp.server.com` in your **dns** or **/etc/hosts** ?
-> [DNS Wikipedia](http://en.wikipedia.org/wiki/Domain_Name_System)
is `my.smtp.server.com` a real (smtp-)server ?
have tried a telnet to port 25 of `my.smtp.server.com` ?
firewall problems ?
if you need a test-server -> [lamson](http://lamsonproject.org/)
|
Netbeans + sqlite3 = Fail?
Question: I've decided to give Python a try on Netbeans. The problem so far is when try
to run program _I know_ works, i.e. if I ran it through the terminal. For the
project I selected the correct Python version (2.6.5). And received the
following error:
> Traceback (most recent call last): File
> "/Users/XXX/NetBeansProjects/NewPythonProject3/src/newpythonproject3.py",
> line 4, in import sqlite3 ImportError: No module named sqlite3
Answer: Search for PYTHONPATH. You probably have different settings in your OS and
Netbeans.
|
Python splitting list based on missing numbers in a sequence
Question: I am looking for the most pythonic way of splitting a list of numbers into
smaller lists based on a number missing in the sequence. For example, if the
initial list was:
seq1 = [1, 2, 3, 4, 6, 7, 8, 9, 10]
the function would yield:
[[1, 2, 3, 4], [6, 7, 8, 9, 10]]
or
seq2 = [1, 2, 4, 5, 6, 8, 9, 10]
would result in:
[[1, 2], [4, 5, 6], [8, 9, 10]]
Answer: From the [python
documentation](http://docs.python.org/library/itertools.html#itertools-
example):
>>> # Find runs of consecutive numbers using groupby. The key to the solution
>>> # is differencing with a range so that consecutive numbers all appear in
>>> # same group.
>>> data = [ 1, 4,5,6, 10, 15,16,17,18, 22, 25,26,27,28]
>>> for k, g in groupby(enumerate(data), lambda (i,x):i-x):
... print map(itemgetter(1), g)
...
[1]
[4, 5, 6]
[10]
[15, 16, 17, 18]
[22]
[25, 26, 27, 28]
The groupby() function from the itertools module generates a break every time
the key function changes its return value. The trick is that the return value
is the number in the list minus the position of the element in the list. This
difference changes when there is a gap in the numbers.
The itemgetter() function is from the [operator
module](http://docs.python.org/library/operator.html#operator.itemgetter),
you'll have to import this and the itertools module for this example to work.
Full example with your data:
>>> from operator import itemgetter
>>> from itertools import *
>>> seq2 = [1, 2, 4, 5, 6, 8, 9, 10]
>>> list = []
>>> for k, g in groupby(enumerate(seq2), lambda (i,x):i-x):
... list.append(map(itemgetter(1), g))
...
>>> print list
[[1, 2], [4, 5, 6], [8, 9, 10]]
Or as a list comprehension:
>>> [map(itemgetter(1), g) for k, g in groupby(enumerate(seq2), lambda (i,x):i-x)]
[[1, 2], [4, 5, 6], [8, 9, 10]]
|
How do I pipe the output of file to a variable in Python?
Question: How do I pipe the output of file to a variable in Python?
Is it possible? Say to pipe the output of `netstat` to a variable x in Python?
Answer: It is possible. See:
<http://docs.python.org/library/subprocess.html#replacing-bin-sh-shell-
backquote>
In Python 2.4 and above:
from subprocess import *
x = Popen(["netstat", "-x", "-y", "-z"], stdout=PIPE).communicate()[0]
|
python human readable large numbers
Question: is there a python library that would make numbers such as this more human
readable
$187,280,840,422,780
edited: for example iw ant the output of this to be 187 Trillion not just
comma separated. So I want output to be trillions, millions, billions etc
Answer: As I understand it, you only want the 'most significant' part. To do so, use
`floor(log10(abs(n)))` to get number of digits and then go from there.
Something like this, maybe:
import math
millnames = ['',' Thousand',' Million',' Billion',' Trillion']
def millify(n):
n = float(n)
millidx = max(0,min(len(millnames)-1,
int(math.floor(0 if n == 0 else math.log10(abs(n))/3))))
return '{:.0f}{}'.format(n / 10**(3 * millidx), millnames[millidx])
Running the above function for a bunch of different numbers:
for n in (1.23456789 * 10**r for r in range(-2, 19, 1)):
print('%20.1f: %20s' % (n,millify(n)))
0.0: 0
0.1: 0
1.2: 1
12.3: 12
123.5: 123
1234.6: 1 Thousand
12345.7: 12 Thousand
123456.8: 123 Thousand
1234567.9: 1 Million
12345678.9: 12 Million
123456789.0: 123 Million
1234567890.0: 1 Billion
12345678900.0: 12 Billion
123456789000.0: 123 Billion
1234567890000.0: 1 Trillion
12345678900000.0: 12 Trillion
123456789000000.0: 123 Trillion
1234567890000000.0: 1235 Trillion
12345678899999998.0: 12346 Trillion
123456788999999984.0: 123457 Trillion
1234567890000000000.0: 1234568 Trillion
|
Python regex confused by brackets ([])?
Question: Is python confused, or is the programmer?
I've got a lot of lines of this:
some_dict[0x2a] = blah
some_dict[0xab] = blah, blah
What I'd like to do is to convert the hex codes into all uppercase to look
like this:
some_dict[0x2A] = blah
some_dict[0xAB] = blah, blah
So I decided to call in the regular expressions. Normally, I'd just do this
using my editor's regexps (xemacs), but the need to convert to uppercase
pushes one into Lisp. ....ok... how about Python?
So I whip together a short script which doesn't work. I've condensed the code
into this example, which doesn't work either. It looks to me like Python's
regexps are getting confused by the brackets in the code. Is it me or Python?
import fileinput
import sys
import re
this = "0x2a"
that = "[0x2b]"
for line in [this, that]:
found = re.match("0x([0-9,a-f]{2})", line)
if found:
print("Found: %s" % found.group(0))
(I'm using the () grouping constructs so I don't capitalize the 'x' in '0x'.)
This example only prints the 0x2a value, not the 0x2b. Is this correct
behavior?
I can easily work around this by changing the match expression to:
found = re.match("\[0x([0-9,a-f]{2}\])", line)
but I'm just wondering if someone can give me some insight into what's going
on here.
Running Python 2.6.2 on Linux.
Answer: `re.match` matches from the _start_ of the string. Use `re.search` instead to
"match the first occurrence anywhere in the string". The key bit about this in
the docs is [here](https://docs.python.org/2/library/re.html#search-vs-match).
|
How to create a Cocoa library and use it in python
Question: I've been making a game and the python library I was used is terrible
(Pyglet). I want to try using Cocoa for the OSX version.
I'll be able to figure out using the objects from classes like NSWindow and
NSOpenGLView and then put these objects in my own class for the game loop.
I have no idea how I can use PyObjC to load a dynamic Objective-C library I
can make and then use the class I will make in python to setup the game which
I suppose can be looped by NSTimer.
However, the loop method will also need to call a python method from one of
many python classes. My game consists of many python classes which are used
for different sections of the game (Mapmaker,GameSession,AnacondaGame etc.).
The game loop will need to call a loop method in any of these classes
depending on the current section and pass even information.
PyObjC is "bi-directional" apparently so how is that done?
Alternatively I could create two methods to be called by python and I add the
python code in-between, where the loop is controlled by python.
The "documentation" on the PyObjC website only seem to explain how to use
Cocoa in python and nothing else.
What I can't do is make a fixed GUI with the interface builder because the
library will need to create windows based on the python input to an
initialisation method of my class.
Knowing the syntax of Objective-C isn't a big problem and I can reefer to the
Cocoa documentation to make the objects I require.
Thank you for any help. It will be appreciated very much. I'm sick of using
broken libraries like pygame and pyglet, using the platform specific OS APIs
seems to be the best method to ensure quality.
Answer: PyObjC bridges Python to the Objective-C runtime, so if you create NSObject
subclasses in Python, they'll be accessible from Objective-C code running in
the same process. What this means is that you'll need to encapsulate all of
your Python functionality in a subclass of NSObject that you can access over
the bridge.
The way I'd do this is by having a singleton controller class on the
Objective-C side that has a method like `-(void)pythonReady:(PythonClass
*)pythonObject`, and also handles the loading of the Python code (which
ensures that the controller class exists when your Python code is loaded).
Then, in your Python code, after creating an instance of your PythonClass, you
can call `pythonReady:` on your controller singleton. Then, in `pythonReady:`
on the Objective-C side, you can call whatever methods you need on
`pythonObject`, which will run the code on the Python side.
To load the Python code from your controller class, you can do something like
this:
#import <Python/Python.h>
@implementation PythonController (Loading)
- (void)loadPython {
NSString *pathToScript = @"/some/path/to/script.py";
setenv("PYTHONPATH", [@"/some/path/to/" UTF8String], 1);
Py_SetProgramName("/usr/bin/python");
Py_Initialize();
FILE *pyScript = fopen([pathToScript UTF8String], "r");
int result = PyRun_SimpleFile(pyScript, [[pathToScript lastPathComponent] UTF8String]);
if (result != 0) { NSLog(@"Loading Python Failed!"); }
}
@end
Basically, we simply use the Python C API to run the script inside the current
process. The script itself starts the bridge to the runtime in the current
process, where you can then use the Cocoa API to access your controller
singleton.
|
Django web interface to store queries and define context
Question: I'm open to persuasion that this is a bad idea. But if not, here's the general
draw:
1. Web interface to maintain data (django.contrib.admin).
2. Web interface to create pages (django.contrib.flatpages)
3. Web interface to create templates ([dbtemplates](http://packages.python.org/django-dbtemplates/index.html))
4. **Where is the web interface to create queries and define context?** (contexts?)
**EDIT**
* * *
Here's the normal situation for Django site development. You have a new page
to make, figure out the url for it, figure out what data is needed to support
the page, then create the appropriate templates so the data is presented the
way you intend.
What I'd like is to be able to do is define what data is needed to support the
page from the admin interface; essentially what you put into a views.py file.
I imagine there being a wrapper view that handles auth, but receives all of
its context from a model (table).
from dbcontext import DBContext # this is fictitious
def db_context_view(request, **args, **kwargs):
# ...some code to handle auth
context = DBContext.objects.get_context_for_request(request, **args, **kwargs)
return render_to_response('mydbtemplates/example.html', context)
I would be happy to still edit the urls.py file to ensure enough gets passed
to the view so that the DBContext manager can locate the appropriate context
record, perform the desired queries (satisfying any query parameters), and
return the appropriate dictionary for the template to succeed.
Answer: I believe you're looking for the [contenttypes
framework](http://docs.djangoproject.com/en/dev/ref/contrib/contenttypes/).
With the contenttypes framework, you would be able to do something like this:
def db_context_view(request, *args, **kwargs):
# ...some code to handle auth
ct = ContentType.objects.get_for_id(kwargs['content_type_id'])
obj = ct.get_object_for_this_type(pk=kwargs['object_id'])
Using this approach, you could build the view you desire.
|
cannot change font to Helvetica in Matplotlib in Python on Mac OS X 10.6
Question: I am trying to change the matplotlib font to helvetica, which I'd like to use
in a PDF plot. I try the following:
import matplotlib
matplotlib.use('PDF')
import matplotlib.pylab as plt
from matplotlib import rc
plt.rcParams['ps.useafm'] = True
rc('font',**{'family':'sans-serif','sans-serif':['Helvetica']})
plt.rcParams['pdf.fonttype'] = 42
This does not work -- when I run my code with --verbose-debug, I get the
error:
backend WXAgg version 2.8.10.1
/Library/Frameworks/Python.framework/Versions/6.2/lib/python2.6/site-packages/matplotlib/__init__.py:833: UserWarning: This call to matplotlib.use() has no effect
because the the backend has already been chosen;
matplotlib.use() must be called *before* pylab, matplotlib.pyplot,
or matplotlib.backends is imported for the first time.
findfont: Could not match :family=sans-serif:style=normal:variant=normal:weight=normal:stretch=normal:size=medium. Returning /Library/Frameworks/Python.framework/Versions/6.2/lib/python2.6/site-packages/matplotlib/mpl-data/fonts/ttf/Vera.ttf
Assigning font /F1 = /Library/Frameworks/Python.framework/Versions/6.2/lib/python2.6/site-packages/matplotlib/mpl-data/fonts/ttf/Vera.ttf
Embedding font /Library/Frameworks/Python.framework/Versions/6.2/lib/python2.6/site-packages/matplotlib/mpl-data/fonts/ttf/Vera.ttf
Writing TrueType font
So apparently it cannot find Helvetica. I am not sure why. I have Helvetica in
the afm directory of mpl-data, and when matplotlib initiates it reads it and
outputs:
createFontDict: /Library/Frameworks/Python.framework/Versions/6.2/lib/python2.6/site-packages/matplotlib/mpl-data/fonts/afm/Helvetica.afm
Do I need a special .ttf Helvetica font in addition? If so, how can I get it?
I know I have Helvetica on my system since I see it in Illustrator and many
other programs.
I am using Enthought Python distribution as follows:
$ python
Enthought Python Distribution -- http://www.enthought.com
Version: 6.2-2 (32-bit)
Python 2.6.5 |EPD 6.2-2 (32-bit)| (r265:79063, May 28 2010, 15:13:03)
[GCC 4.0.1 (Apple Inc. build 5488)] on darwin
Type "help", "copyright", "credits" or "license" for more information.
>>> import matplotlib
>>> matplotlib.__version__
'0.99.3'
Any ideas how this can be fixed?
thanks.
Answer: The solution is to use fondu to convert the .dfont Helvetica font from Mac OS
X into .ttf, and then place that in the mpl-data/fonts directory that
Matplotlib looks in. That solved the issue.
|
Python: Load module by its name
Question: I'm working on a django project that serves multiple sites; depending on the
site I want to import different functionality from a different module; how do
I import a module in Python if I have the name of its package and the module
name itself as a string?
Answer: in Python generally, you can use `__import__` builtin function or `imp` module
features:
>>> sys1 = __import__("sys")
>>> import imp
>>> sys2 = imp.load_module("sys2", *imp.find_module("sys"))
>>> import sys
>>> sys is sys1 is sys2
True
|
reading file data mixing strings and numbers in python
Question: I would like to read different files in one directory with the following
structure:
# Mj = 1.60 ff = 7580.6 gg = 0.8325
I would like to read the numbers from each file and associate every one to a
vector. If we assume I have 3 files, I will have 3 components for vector Mj,
... How can I do it in Python?
Thanks for your help.
Answer: I'd use a regular expression to take the line apart:
import re
lineRE = re.compile(r'''
\#\s*
Mj\s*=\s*(?P<Mj>[-+0-9eE.]+)\s*
ff\s*=\s*(?P<ff>[-+0-9eE.]+)\s*
gg\s*=\s*(?P<gg>[-+0-9eE.]+)
''', re.VERBOSE)
for filename in filenames:
for line in file(filename, 'r'):
m = lineRE.match(line)
if not m:
continue
Mj = m.group('Mj')
ff = m.group('ff')
gg = m.group('gg')
# Put them in whatever lists you want here.
|
Python geocode filtering by distance
Question: I need to filter geocodes for near-ness to a location. For example, I want to
filter a list of restaurant geocodes to identify those restaurants within 10
miles of my current location.
Can someone point me to a function that will convert a distance into latitude
& longitude deltas? For example:
class GeoCode(object):
"""Simple class to store geocode as lat, lng attributes."""
def __init__(self, lat=0, lng=0, tag=None):
self.lat = lat
self.lng = lng
self.tag = None
def distance_to_deltas(geocode, max_distance):
"""Given a geocode and a distance, provides dlat, dlng
such that
|geocode.lat - dlat| <= max_distance
|geocode.lng - dlng| <= max_distance
"""
# implementation
# uses inverse Haversine, or other function?
return dlat, dlng
Note: I am using the supremum norm for distance.
Answer: There seems not to have been a good Python implementation. Fortunately the SO
"Related articles" sidebar is our friend. [This SO
article](http://stackoverflow.com/questions/1689096/calculating-bounding-box-
a-certain-distance-away-from-a-lat-long-coordinate-in-ja) points to an
[excellent
article](http://janmatuschek.de/LatitudeLongitudeBoundingCoordinates) that
gives the maths and a Java implementation. The actual function that you
require is rather short and is embedded in my Python code below. Tested to
extent shown. Read warnings in comments.
from math import sin, cos, asin, sqrt, degrees, radians
Earth_radius_km = 6371.0
RADIUS = Earth_radius_km
def haversine(angle_radians):
return sin(angle_radians / 2.0) ** 2
def inverse_haversine(h):
return 2 * asin(sqrt(h)) # radians
def distance_between_points(lat1, lon1, lat2, lon2):
# all args are in degrees
# WARNING: loss of absolute precision when points are near-antipodal
lat1 = radians(lat1)
lat2 = radians(lat2)
dlat = lat2 - lat1
dlon = radians(lon2 - lon1)
h = haversine(dlat) + cos(lat1) * cos(lat2) * haversine(dlon)
return RADIUS * inverse_haversine(h)
def bounding_box(lat, lon, distance):
# Input and output lats/longs are in degrees.
# Distance arg must be in same units as RADIUS.
# Returns (dlat, dlon) such that
# no points outside lat +/- dlat or outside lon +/- dlon
# are <= "distance" from the (lat, lon) point.
# Derived from: http://janmatuschek.de/LatitudeLongitudeBoundingCoordinates
# WARNING: problems if North/South Pole is in circle of interest
# WARNING: problems if longitude meridian +/-180 degrees intersects circle of interest
# See quoted article for how to detect and overcome the above problems.
# Note: the result is independent of the longitude of the central point, so the
# "lon" arg is not used.
dlat = distance / RADIUS
dlon = asin(sin(dlat) / cos(radians(lat)))
return degrees(dlat), degrees(dlon)
if __name__ == "__main__":
# Examples from Jan Matuschek's article
def test(lat, lon, dist):
print "test bounding box", lat, lon, dist
dlat, dlon = bounding_box(lat, lon, dist)
print "dlat, dlon degrees", dlat, dlon
print "lat min/max rads", map(radians, (lat - dlat, lat + dlat))
print "lon min/max rads", map(radians, (lon - dlon, lon + dlon))
print "liberty to eiffel"
print distance_between_points(40.6892, -74.0444, 48.8583, 2.2945) # about 5837 km
print
print "calc min/max lat/lon"
degs = map(degrees, (1.3963, -0.6981))
test(*degs, dist=1000)
print
degs = map(degrees, (1.3963, -0.6981, 1.4618, -1.6021))
print degs, "distance", distance_between_points(*degs) # 872 km
|
Failure loading py2exe'd program when including pysvn
Question: I am attempting to run a py2exe'd program (package.py) that includes pysvn. It
is failing to run with the following error:
Traceback (most recent call last):
File "package.py", line 27, in <module>
File "zipextimporter.pyc", line 82, in load_module
File "pysvn\__init__.pyc", line 99, in <module>
File "zipextimporter.pyc", line 98, in load_module
ImportError: MemoryLoadLibrary failed loading pysvn\_pysvn_2_6.pyd
The script runs fine for others in the office, the difference being I'm on
Windows 7 x64 with them on WinXP x86. I do have _pysvn_2_6.pyd in my pysvn
directory.
Py2exe's "Problems to be Fixed" page has a similar error message with WxPython
where it cannot find a needed system module, but I am not using WxPython and I
have the dll they refer to anyway.
The py2exe page for "Working with Various Packages and Modules" doesn't refer
to pysvn, and I can't find anyone else with similar problems.
I've checked the output of py2exe as outlined by [this
answer](http://stackoverflow.com/questions/1048651/problem-deploying-python-
program-packaged-with-py2exe/1124797#1124797), but my computer seems to have
all the binary files required in the correct locations.
EDIT: I just tried to run other py2exe created programs on this same machine
and they failed as well. It seems that the problem is with my machine (ie x64)
rather than the specific program I was converting; I get a similar error with
another program:
Traceback (most recent call last):
File "rundemo.py", line 13, in <module>
import win32api as w32
File "zipextimporter.pyc", line 98, in load_module
ImportError: MemoryLoadLibrary failed loading win32api.pyd
EDIT2: I tried the py2exe programs generated from my 64 bit compy on a 32 bit
machine, and they failed with the same error. I think I'm generating 32 bit
exe's (py2exe docs say 64-bit support is experimental, and I haven't
explicitly turned it on), but I'm not sure how to check to be sure.
Answer: Install [PyWin32](http://starship.python.net/~skippy/).
|
catch specific HTTP error in python
Question: I want to catch a specific http error and not any one of the entire family..
what I was trying to do is --
import urllib2
try:
urllib2.urlopen("some url")
except urllib2.HTTPError:
<whatever>
but what I end up is catching any kind of http error, but I want to catch only
if the specified webpage doesn't exist!! probably that's HTTP error 404..but I
don't know how to specify that catch only error 404 and let the system run the
default handler for other events..ny suggestions??
Answer: Just catch `urllib2.HTTPError`, handle it, and if it's not Error 404, simply
use `raise` to re-raise the exception.
See the [Python
tutorial](http://docs.python.org/tutorial/errors.html#handling-exceptions).
So you could do:
import urllib2
try:
urllib2.urlopen("some url")
except urllib2.HTTPError as err:
if err.code == 404:
<whatever>
else:
raise
|
Can you pass multiple paths to the Django runserver --pythonpath directive?
Question: For each of my projects I create an apps directory that holds all the apps I
need. Satchmo also has an apps directory. Can I do something like _python
manage.py runserver --pythonpath=/path/to/my/apps /path/to/satchmo/apps_? Is
there some separator that it can take?
Answer: There's no `--pythonpath` option to runserver. You either want to add it to
your `.bashrc` file or in your `settings.py` file add something like the
following at the top:
import os,sys
PROJECT_ROOT = os.path.realpath(os.path.dirname(__file__))
sys.path.append(PROJECT_ROOT, 'to', 'my', 'apps')
sys.path.append(os.path.join('path', 'to', 'satchmo', 'apps'))
|
Python socket server craps out after receiving data
Question: I'm currently dabbling in sockets.
I've got a jquery script that uses a very small flash swf file to establish a
true socket connection. As a server I'd like to use python.
Everything works, but I can only send information to the server just once.
I've tried 2 pieces of python code for the server.
I guess since they both have the same problem the problem's not here.
# TCP server example
import socket
server_socket = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
server_socket.bind(("", 2000))
server_socket.listen(5)
print "TCPServer Waiting for client on port 2000"
while 1:
client_socket, address = server_socket.accept()
print "I got a connection from ", address
while 1:
data = client_socket.recv(512)
print "RECIEVED:" , data
Or this one:
import socket
mySocket = socket.socket ( socket.AF_INET, socket.SOCK_STREAM )
mySocket.bind ( ( '', 2000 ) )
mySocket.listen ( 1 )
while True:
channel, details = mySocket.accept()
print 'We have opened a connection with', details
print channel.recv ( 100 )
channel.close()
On the client side I use <http://devpro.it/xmlsocket/>
Sending a piece of data is as simple as executing
xmls.send('some text');
Which arrives, but after that it stops working.
Does anyone know a solution? Or possibly a better javascript/swf combination I
could use?
Answer: I think you need to 'listen' again after you close the connection. Also,
Sockets deliver data as per the tcp specifications. You're not guaranteed to
get all of any data sent in one socket read. I see nothing to perform multiple
reads and assemble a complete 'message'
|
How to use nose with IronPython?
Question: I installed nose using the 'setup.py install' on the command line , I am able
to run 'nosetests' and any python file matching testMatch regular expression
is picked up and tests are automated in the %python home%\Scripts directory.
Now I want nose to work with my iron Python files , how do I install nose on
the %Iron Python home% directory ? i noticed my Iron Python Home directory
does not even have a Scripts folder. If i try running 'nosetests' with iron
python code , it throws all sorts of exception for eg. no module named clr.
Is anybody using nose with iron python ? if yes , please guide me. I have been
struggling with this since an entire day, currently my only workaround has
been adding the following in my IronPython code:
import nose
nose.main(argv=['<arguments>'])
is this is the only way to go about using nose in iron python files ?
if there is no other way , then I wanted to know how to use the several
plugins that nose has ? especially the coverage plugin ? i installed it for
python2.6 , but how to make it work for ironpython ?
The reason I am asking is because with python , it gets easy to use the
plugins just by calling the command line , but with IronPython I don't know
how to make it work.
Answer: Your solution is actually all [`nosetests`](http://python-
nose.googlecode.com/hg/bin/nosetests) does:
#!/usr/bin/env python
from nose import main
if __name__ == '__main__':
main()
You'll want to make sure you add your system's Python lib to the path for it
to find the nose extensions:
>>>import sys
>>>sys.path.append(r'C:\Python26\lib')
And you'll need to make sure you're executing your script with `ipy.exe` and
not your system's Python executable.
|
How to read String in java that was written using python’s struct.pack method
Question:
out.write( struct.pack(">f", 1.1) );
out.write( struct.pack(">i", 12) );
out.write( struct.pack(">3s", "abc") );
how to import struct package in java it says ..
> no package found when i am trying to execute it
so kindly tell me any suggestions if any
Thanking you
i took that code from <http://stackoverflow.com/questions/1255918/how-to-read-
string-in-java-that-was-written-using-pythons-struct-pack-method>
Answer: Read the answer to the question you referenced. The sample code in the
question was incorrect.
Also, you don't import the struct package in Java. It's a Python package. Also
as described in the other question, you use java.io.DataInputStream to read
the file created from Python.
|
How to synchronize the output of Python subprocess
Question: I think I'm having issues to synchronize the output of two Popen running
concurrently. It seems that the output from these two different command lines
are interleaved with one another. I also tried using RLock to prevent this
from happening but it didn't work.
A sample output would be:
cmd1
cmd1
cmd2
cmd2
cmd2
cmd2
cmd1
cmd2
The code is as attached:
import subprocess
import threading
class PopenWorkerThread(threading.Thread):
def __init__(self, cmdLine):
self.lock = threading.RLock()
self.WebSphereCmdLine = cmdLine
threading.Thread.__init__(self)
def run(self):
logger.error('Runninf: ' + self.WebSphereCmdLine)
proc = subprocess.Popen(self.WebSphereCmdLine, shell=False, stdout=subprocess.PIPE)
while True:
self.lock.acquire()
print proc.stdout.readline()
self.lock.release()
def launch():
commandLine = ['ls -l', 'netstat']
for cmdLine in commandLine:
workerThread = PopenWorkerThread(cmdLine)
workerThread.start()
launch()
Is there a way to synchronize the outputs so that they look like such?
cmd1
cmd1
cmd1
cmd1
cmd1
cmd2
cmd2
cmd2
cmd2
cmd2
Answer: You're locking with a granularity of a line, so of course lines from one
thread can and do alternate with lines from the other. As long as you're
willing to wait until a process ends before showing any of its output, you can
lock with the larger "process" granularity. Of course you have to use the SAME
lock for both threads -- having each thread use a completely separate lock, as
you're doing now, cannot achieve anything at all, obviously.
So, for example:
import subprocess import threading
class PopenWorkerThread(threading.Thread):
lock = threading.RLock() # per-class, NOT per-instance!
def __init__(self, cmdLine):
self.WebSphereCmdLine = cmdLine
threading.Thread.__init__(self)
def run(self):
logger.error('Runninf: ' + self.WebSphereCmdLine)
proc = subprocess.Popen(self.WebSphereCmdLine, shell=False, stdout=subprocess.PIPE)
result, _ = proc.communicate()
with self.lock:
print result,
def launch(): commandLine = ['ls -l', 'netstat'] for cmdLine in commandLine:
workerThread = PopenWorkerThread(cmdLine) workerThread.start()
launch()
|
Class design — circular references between related classes
Question: I need help trying to figure out the proper design of my classes.
I have a user class:
class AppUser:
_email - String
_fullname - String
_organizations - List of ????
_active - Boolean
------------------
getOrgs - Method
Also, I have an Organizations class:
class Organization:
_name - String
_domain - String
_members - List of ????
------------------
getMembers
So, my issue is the Lists. The Org class has a list of _members. This list
should probably be a list of AppUser objects. And, the AppUser class has a
list of _organizations. This list should probably be a list of Organization
objects.
But this would create a circular reference.
So, how should I implement this?
Edit: Need to implement this using Python.
Answer: You did not specify which language you were using. That is important because
in some languages circular references do cause problems (VB6) while in others
they do not (Java, C#, etc.). In most cases you will be okay with circular
references in your class hierarchies especially if you are using a modern
language that uses garbage collection for memory management.
|
How to generate an HMAC in Java equivalent to a Python example?
Question: I'm looking at implementing an app getting [Twitter authorization via
Oauth](http://apiwiki.twitter.com/Authentication) in Java. The first step is
[getting a request token](http://apiwiki.twitter.com/Twitter-REST-API-
Method%3A-oauth-request_token). Here is a [Python
example](http://github.com/tav/tweetapp/blob/master/standalone/twitter_oauth_handler.py)
for app engine.
To test my code, I am running Python and checking output with Java. Here is an
example of Python generating a Hash-Based Message Authentication Code (HMAC):
#!/usr/bin/python
from hashlib import sha1
from hmac import new as hmac
key = "qnscAdgRlkIhAUPY44oiexBKtQbGY0orf7OV1I50"
message = "foo"
print "%s" % hmac(key, message, sha1).digest().encode('base64')[:-1]
Output:
$ ./foo.py
+3h2gpjf4xcynjCGU5lbdMBwGOc=
How does one replicate this example in Java?
I've seen an [example of
HMAC](http://exampledepot.8waytrips.com/egs/javax.crypto/GenMac.html) in Java:
try {
// Generate a key for the HMAC-MD5 keyed-hashing algorithm; see RFC 2104
// In practice, you would save this key.
KeyGenerator keyGen = KeyGenerator.getInstance("HmacMD5");
SecretKey key = keyGen.generateKey();
// Create a MAC object using HMAC-MD5 and initialize with key
Mac mac = Mac.getInstance(key.getAlgorithm());
mac.init(key);
String str = "This message will be digested";
// Encode the string into bytes using utf-8 and digest it
byte[] utf8 = str.getBytes("UTF8");
byte[] digest = mac.doFinal(utf8);
// If desired, convert the digest into a string
String digestB64 = new sun.misc.BASE64Encoder().encode(digest);
} catch (InvalidKeyException e) {
} catch (NoSuchAlgorithmException e) {
} catch (UnsupportedEncodingException e) {
}
It uses
[javax.crypto.Mac](http://download.oracle.com/docs/cd/E17409_01/javase/6/docs/api/javax/crypto/Mac.html),
all good. However, the
[SecretKey](http://download.oracle.com/docs/cd/E17409_01/javase/6/docs/api/javax/crypto/SecretKey.html)
constructors take bytes and an algorithm.
What's the algorithm in the Python example? How can one create a Java secret
key without an algorithm?
Answer: HmacSHA1 seems to be the algorithm name you need:
SecretKeySpec keySpec = new SecretKeySpec(
"qnscAdgRlkIhAUPY44oiexBKtQbGY0orf7OV1I50".getBytes(),
"HmacSHA1");
Mac mac = Mac.getInstance("HmacSHA1");
mac.init(keySpec);
byte[] result = mac.doFinal("foo".getBytes());
BASE64Encoder encoder = new BASE64Encoder();
System.out.println(encoder.encode(result));
produces:
+3h2gpjf4xcynjCGU5lbdMBwGOc=
Note that I've used `sun.misc.BASE64Encoder` for a quick implementation here,
but you should probably use something that doesn't depend on the Sun JRE. [The
base64-encoder in Commons
Codec](http://commons.apache.org/codec/apidocs/org/apache/commons/codec/binary/Base64.html)
would be a better choice, for example.
|
No module named django.core
Question: I'm following the step by step guide
[here](http://jeffbaier.com/articles/installing-django-on-an-ubuntu-linux-
server/) and I hit an error at the "Create Django Project" step when I try the
command;
> django-admin.py startproject myproject
The error:
> Traceback (most recent call last):
> File "/usr/local/bin/django-admin.py", line 2, in from django.core import
> management ImportError: No module named django.core
Running on Ubuntu Server with Python 2.6.
I'm sure it's a really simple error, and something do with Python paths, but
I'm a Linux newbie. Thanks!
Answer: Thanks to Daniel Roseman's comment, I investigated and found my symlink was
broken. Just had to recreate that and it worked nicely.
|
append a particular column from a csv file to another using python
Question: I'll explain my whole problem:
I have 2 csv files:
* project-table.csv (has about 50 columns)
* interaction-matrix.csv (has about 45 columns)
I want to append the string in `col[43]` from project-table.csv with string in
`col[1]` of interaction-matrix.csv with a dot(`.`) in between both the strings
next,
* interaction-matrix.csv has a set of headers..
* its 1st col will now have the appended string after doing what I've mentioned above
* all other remaining columns have only 0's and 1's
* I'm supposed to extract only those columns with 1's from this interaction-matrix.csv and copy it to a new csv file... (with the first column intact)
this is the code i ve come up with...
I'm getting an error with the `keepcols` line...
import csv
reader=csv.reader(open("project-table.csv","r"))
writer=csv.writer(open("output.csv","w"),delimiter=" ")
for data in reader:
name1=data[1].strip()+'.'+data[43].strip()
writer.writerow((name1, None))
reader=csv.DictReader(open("interaction-matrix.csv","r"),[])
allrows = list(reader)
keepcols = [c for c in allrows[0] if all(r[c] != '0' for r in allrows)]
print keepcols
writer=csv.DictWriter(open("output1.csv","w"),fieldnames='keepcols',extrasaction='ignore')
writer.writerows(allrows)
this is the error i get:
Traceback (most recent call last):
File "prg1.py", line 23, in ?
keepcols = [c for c in allrows[0] if all([r[c] != '0' for r in allrows])]
NameError: name 'all' is not defined
project table and interaction-matrix both have the same data in their
respective 1st columns .. so i just appended col[43] of prj-table to col[1] of
the same table itself...
Answer: Edit your question to show what error message are you getting. Update:
NameError probably means you are using an (older) version of Python (which
one?) without `all()` or (you have used `all` as a variable name AND are not
showing the exact code that you ran)
Note: open both files in binary mode ("rb" and "wb") respectively.
You say "I want to append the string in col[43] from project-table.csv with
string in col[1] of interaction-matrix.csv with a dot(.) in between both the
strings" HOWEVER you are using col[2] (not col[1]) of project-table.csv (not
interaction-matrix.csv, which you haven't opened at that stage).
|
Extract Meta Keywords From Webpage?
Question: I need to extract the meta keywords from a web page using Python. I was
thinking that this could be done using urllib or urllib2, but I'm not sure.
Anyone have any ideas?
I am using Python 2.6 on Windows XP
Answer: [lxml](http://codespeak.net/lxml/index.html#documentation) is faster than
BeautifulSoup (I think) and has much better functionality, while remaining
relatively easy to use. Example:
52> from urllib import urlopen
53> from lxml import etree
54> f = urlopen( "http://www.google.com" ).read()
55> tree = etree.HTML( f )
61> m = tree.xpath( "//meta" )
62> for i in m:
..> print etree.tostring( i )
..>
<meta http-equiv="content-type" content="text/html; charset=ISO-8859-2"/>
Edit: another example.
75> f = urlopen( "http://www.w3schools.com/XPath/xpath_syntax.asp" ).read()
76> tree = etree.HTML( f )
85> tree.xpath( "//meta[@name='Keywords']" )[0].get("content")
85> "xml,tutorial,html,dhtml,css,xsl,xhtml,javascript,asp,ado,vbscript,dom,sql,colors,soap,php,authoring,programming,training,learning,b
eginner's guide,primer,lessons,school,howto,reference,examples,samples,source code,tags,demos,tips,links,FAQ,tag list,forms,frames,color table,w3c,cascading
style sheets,active server pages,dynamic html,internet,database,development,Web building,Webmaster,html guide"
BTW: [XPath](http://www.w3schools.com/XPath/xpath_syntax.asp) is worth
knowing.
Another edit:
Alternatively, you can just use regexp:
87> f = urlopen( "http://www.w3schools.com/XPath/xpath_syntax.asp" ).read()
88> import re
101> re.search( "<meta name=\"Keywords\".*?content=\"([^\"]*)\"", f ).group( 1 )
101>"xml,tutorial,html,dhtml,css,xsl,xhtml,javascript,asp,ado,vbscript,dom,sql, ...etc...
...but I find it less readable and more error prone (but involves only
standard module and still fits on one line).
|
Import large chunk of data into Google App Engine Data Store at one go
Question: I have a large CSV file, approx 10 MB in size, which contains all the data
which need to be imported in the Google App Engine DataStore. I tried
following approaches to perform import but all the times it failed in half
way.
* Import using mapping a command to url and then executing url, failed because of request time out...
* Import using creating cron job, but got DeadlineExceededError...
* Import using remort_api_shell, but got Operation timed out.
Can you please suggest me and approch (using dummy data you can imagine) how
to do it... Suggestion with code will be more helpful..
** I am using Python and google's web app framework to develop the said app.
Answer: you can post row by row. using built in bulk loader.
<http://code.google.com/appengine/docs/python/tools/uploadingdata.html>
this is good article.
and here is my contactloader.py that i used 2 years ago for reference. it is
more sophisticated since last i used but still.....
import datetime
from google.appengine.ext import db
from google.appengine.tools import bulkloader
class Contact(db.Model):
date = db.DateTimeProperty(auto_now_add=True)
owner = db.StringProperty()
companyname = db.StringProperty()
companyemail = db.EmailProperty()
def myfunc(x):
temp = x.split(":mailto:")
if len(temp) > 0:
temp = temp[-1].split(":")
else:
return "defaultvalue"
if len(temp) > 0:
temp = temp[0]
else:
return "defaultvalue"
temp = temp.split("<1>")[0]
if temp is None or len(temp) < 5:
return "defaultvalue"
return temp
def mysecfunc(x):
return x.split("<0>")[0]
class ContactLoader(bulkloader.Loader):
def __init__(self):
bulkloader.Loader.__init__(self, 'Contact',
[
('companyname',mysecfunc),
('owner', lambda x:"somevalue"),
('companyemail',myfunc),
("date",lambda x:datetime.datetime.now()),
])
loaders = [ContactLoader]
|
Read all the contents in ini file into dictionary with Python
Question: Normally, I code as follows for getting a particular item in a variable as
follows
try:
config = ConfigParser.ConfigParser()
config.read(self.iniPathName)
except ConfigParser.MissingSectionHeaderError, e:
raise WrongIniFormatError(`e`)
try:
self.makeDB = config.get("DB","makeDB")
except ConfigParser.NoOptionError:
self.makeDB = 0
Is there any way to read all the contents in a python dictionary?
For example
[A]
x=1
y=2
z=3
[B]
x=1
y=2
z=3
is written into
val["A"]["x"] = 1
...
val["B"]["z"] = 3
Answer: I suggest subclassing `ConfigParser.ConfigParser` (or `SafeConfigParser`, &c)
to safely access the "protected" attributes (names starting with single
underscore -- "private" would be names starting with _two_ underscores, not to
be accessed even in subclasses...):
import ConfigParser
class MyParser(ConfigParser.ConfigParser):
def as_dict(self):
d = dict(self._sections)
for k in d:
d[k] = dict(self._defaults, **d[k])
d[k].pop('__name__', None)
return d
This emulates the usual logic of config parsers, and is guaranteed to work in
all versions of Python where there's a `ConfigParser.py` module (up to 2.7,
which is the last of the `2.*` series -- knowing that there will be no future
Python 2.any versions is how compatibility can be _guaranteed_ ;-).
If you need to support future Python `3.*` versions (up to 3.1 and probably
the soon forthcoming 3.2 it should be fine, just renaming the module to all-
lowercase `configparser` instead of course) it may need some attention/tweaks
a few years down the road, but I wouldn't expect anything major.
|
Get a subset of a generator
Question: I have a generator function and want to get the first ten items from it; my
first attempt was:
my_generator()[:10]
This doesn't work because generators aren't subscriptable, as the error tells
me. Right now I have worked around that with:
list(my_generator())[:10]
This works since it converts the generator to a list; however, it's
inefficient and defeats the point of having a generator. Is there some built-
in, Pythonic equivalent of `[:10]` for generators?
Answer:
import itertools
itertools.islice(mygenerator(), 10)
`itertools` has a number of utilities for working with iterators. `islice`
takes start, stop, and step arguments to slice an iterator just as you would
slice a list.
|
Jinja2: Looking for a View-Helper
Question: I'am new to the Jinja2 template engine. Is there something like the view-
helpers from Zend Framework? Can i create simple functions and reuse them all
over all my template-files?
Something like this?
#somewhere in my python code:
def nice_demo_function(message):
""""return a simple message"""
return message
So i can to use that:
<!-- now in my template-file -->
{% nice_demo_function('yes, this works great!') %}
Answer: There are a number of ways you can expose helper functions to your templates.
You could define them using
[macros](http://jinja.pocoo.org/2/documentation/templates#macros), and then
[import](http://jinja.pocoo.org/2/documentation/templates#import) them into
templates that use them. You could add functions to the [globals
attribute](http://jinja.pocoo.org/2/documentation/api#jinja2.Template.globals)
of your Template objects, or pass them to the
[render()](http://jinja.pocoo.org/2/documentation/api#jinja2.Template.render)
method. You could subclass Template to do the same without having to repeat
yourself each time. If you want to get really fancy, you could look into
writing [extensions](http://jinja.pocoo.org/2/documentation/extensions#jinja-
extensions) as well (but you probably don't need to go that deep).
|
set process name in mod_wsgi
Question: I'm running a site by apache2.x with mod_wsgi 2.5, and python2.5. It is
configured to run in multi-processes and each process only contains one
thread.
When I read this
[post](http://pragdave.blogs.pragprog.com/pragdave/2008/11/trivial-request-
logging-for-rails.html), I try to set the process name to PATH_INFO, but it
doesn't work. My code is like:
import ctypes
libc = ctypes.CDLL('/lib/libc.so.6')
def application (environ, start_response):
libc.prctl(15, environ.get('PATH_INFO', 'WSGI'), 0, 0, 0);
# other codes
Answer: If you are using mod_wsgi daemon mode, is there anything wrong with the
display-name option to WSGIDaemonProcess. That option is precisely for
changing the name of the process to a fixed value using setproctitle() or
argv[0] assignment as believed works for specific platforms. See:
<http://code.google.com/p/modwsgi/wiki/ConfigurationDirectives#WSGIDaemonProcess>
Note that it only makes sense to do this for daemon mode processes and not the
Apache server processes themselves. Thus why is only available for
WSGIDaemonProcess directive. It only makes sense to set it once on process
start as well and not dynamically based on request.
|
Session management via pure CGI
Question: I'm currently in the process of writing a little blog / generic posting system
using CGI in C as a hobby project and am now in the need of a session
management system to authentificate authorized users for posting, editing and
similar operations over **multiple CGI programs**
From working with PHP years ago I remember using the superglobal variable
`$_SESSION` and some session intializing functions. _Obviously_ this is not
going to work this way when dealing with pure CGI, so I'm in a tricky
situation here.
A bit of thinking showed that there's many different ways to do such a
thing...
1. Saving the IP address and attributes inside a file where I can see if a particular IP is authorized
2. Same as #1 but using an SQLite database (my engine already runs on SQLite so there would be no additional overhead)
3. Something with cookies maybe?
Instead of going all in and regret is later... what do **you** good people
think? What's the most efficient (and most importantly) and the maintainable
method?
Please note that I do _not_ want to get a third party libary to do all the
complicated things for me! I started this project to build something
completely by myself (if you ignore SQLite here) and I don't want to hide the
hard parts, even if it makes everything so much simpler. I could have just
used Python if I didn't want to torture myself :)
Answer: Cookie based session management is the way to go. You cannot merely use an IP
address not even IP address + browser combination because that will fail when
people are using proxy or are behind NAT.
Just send the browser a hash in a cookie, then validate the hash against your
record for the user, if it matches, you can then access the data for that
user's session.
Consider adding an expiry mechanism for the hash. There is a trade off between
security and ease of use, because the longer the same hash is valid for the
user, the longer the user is vulnerable to a cookie stealing attack.
Expiry mechanisms will also enable you to delete stale session data from your
database (or file, if you would so choose.)
|
Weird error when trying to write to an mmap under windows
Question: This simple python code:
import mmap
with file("o:/temp/mmap.test", "w+b") as fp:
m = mmap.mmap(fp.fileno(), 0, access=mmap.ACCESS_READ|mmap.ACCESS_WRITE)
m.write("Hello world!")
Produces the following error (on the mmap.mmap(...) line):
WindowsError: [Error 1006] The volume for a file has been externally altered
so that the opened file is no longer valid
Any idea why?
Answer: Most likely because `w+` truncates the file, and Windows gives an error when
trying to create an empty mapping from that file of length 0. Use `r+`
instead.
As well, you shouldn't use `access=mmap.ACCESS_READ|mmap.ACCESS_WRITE`:
>>> mmap.ACCESS_READ
1
>>> mmap.ACCESS_WRITE
2
>>> mmap.ACCESS_COPY
3
>>> mmap.ACCESS_READ | mmap.ACCESS_WRITE
3
In other words, `access=mmap.ACCESS_READ|mmap.ACCESS_WRITE` is the same as
`access=mmap.ACCESS_COPY`. What you want is most likely
`access=mmap.ACCESS_WRITE`, and on Windows that's what you get anyway if you
don't explicitly use that argument.
Try this:
import mmap
with file("o:/temp/mmap.test", "r+b") as fp:
m = mmap.mmap(fp.fileno(), 0)
m.write("Hello world!")
( mmap docs: <http://docs.python.org/library/mmap.html> )
|
Python Rpy R data processing optimization
Question: I am writing a data processing program in Python and R, bridged with Rpy2.
Input data being binary, I use Python to read data out and pass them to R,
then collect results to output.
Data are organized into pieces, each being around 100 Bytes (1Byte per value *
100 values).
They just work now, but the speed is very low. Here are some of my test on 1GB
size (that is, 10^7 pieces) of data:
If I disable Rpy2 calls to make a dry run, it takes about 90min for Python to
loop all through on a Intel(R) Xeon(TM) CPU 3.06GHz using one single thread.
If I enable full functionality and multithreading on that Xeon dual core, it
(will by estimation) take ~200hrs for the program to finish.
I killed the Python program several times the call stack is almost alwarys
pointing to Rpy2 function interface. I also did profiling, which gives similar
results.
All these observations indicates the R part called by Rpy2 is the bottleneck.
So I profiled a standalone version of my R program, but the profiling summary
points to "Anonymous". I am still pushing my way to see which part of my R
script is the most time consuming one. ***_updated, see my edit below_ ****
There are two suspicious candidates through, one being a continuous wavelets
transformation (CWT) and wavelets transformation modulus maxima (WTMM) using
wmtsa from cran[1], the other being a non-linear fitting of ex-gaussion curve.
What come to my mind are:
1. for fitting, I could substitute R routing with inline C code? there are many fitting library available in C and fortran... (idea from the net; I never did that; unsure)
2. for wavelet algorithms.... I would have to analyze the wmtsa package to rewrite hotspots in C? .... reimplementing the entire wmtsa package using C or fortran would be very non-trivial for me. I have not much programming experience.
3. the data piece in file is organized in 20 consecutive Bytes, which I could map directly to a C-like char* array? at present my Python program just read one Byte at a time and append it to a list, which is slow. This part of code takes 1.5 hrs vs. ~200 hrs for R, so not that urgent.
This is the first time I meet program efficiency in solving real problems . I
STFW and felt overwhelmed by the informations. Please give me some advice for
what to do next and how.
Cheers!
footnotes:
1. <http://cran.r-project.org/web/packages/wmtsa/index.html>
*** Update ***
Thanks to proftools from cran, I managed to create a call stack graph. And I
could see that ~56% of the time are spent on wmtsa, code snippet is like:
W <- wavCWT(s,wavelet="gaussian1",variance=1/p) # 1/4
W.tree <-wavCWTTree(W) # 1/2
holderSpectrum(W.tree) # 1/4
~28% of time is spent on nls:
nls(y ~ Q * dexGAUS(x, m, abs(s), abs(n)) + B, start = list(Q = 1000, m = h$time[i], s = 3, n = 8, B = 0), algorithm="default", trace=FALSE)
where evaluation of dexGAUS from gamlss.dist package takes the majority of
time.
remaining ~10% of R time are spent on data passing/split/aggregation/subset.
Answer: For option 3.. getting your data in efficiently... read it all in as one long
str type in python with a single read from the file. Let's assume it's called
myStr.
import array
myNums = array.array('B', myStr)
Now myNums is an array of each byte easily converted... see
help(array.array)... in fact, looking at that it looks like you can get it
directly from a file that way through the array.
That should get rid of 1.4 hours of your data reading.
|