Package: loxun
loxun is a Python module to write large output in XML using Unicode and
namespaces. Of course you can also use it for small XML output with plain 8
bit strings and no namespaces.loxun’s features are:small memory foot print: the document is created on the fly by writing to
an output stream, no need to keep all of it in memory.easy to use namespaces: simply add a namespace and refer to it using the
standardnamespace:tagsyntax.mix unicode and io.BytesIO: pass both unicode or plain 8 bit strings to any
of the methods. Internally loxun converts them to unicode, so once a
parameter got accepted by the API you can rely on it not causing any
messyUnicodeErrortrouble.automatic escaping: no need to manually handle special characters such
as<or&when writing text and attribute values.robustness: while you write the document, sanity checks are performed on
everything you do. Many silly mistakes immediately result in anXmlError, for example missing end elements or references to undeclared
namespaces.open source: distributed under the GNU Lesser General Public License 3
or later.Here is a very basic example. First you have to create an output stream. In
many cases this would be a file, but for the sake of simplicity we use aio.BytesIOhere:>>> from __future__ import unicode_literals
>>> import io
>>> out = io.BytesIO()Then you can create anXmlWriterto write to this output:>>> xml = XmlWriter(out)Now write the content:>>> xml.addNamespace("xhtml", "http://www.w3.org/1999/xhtml")
>>> xml.startTag("xhtml:html")
>>> xml.startTag("xhtml:body")
>>> xml.text("Hello world!")
>>> xml.tag("xhtml:img", {"src": "smile.png", "alt": ":-)"})
>>> xml.endTag()
>>> xml.endTag()
>>> xml.close()And the result is:>>> print out.getvalue().rstrip("\r\n")
<?xml version="1.0" encoding="utf-8"?>
<xhtml:html xmlns:xhtml="http://www.w3.org/1999/xhtml">
  <xhtml:body>
    Hello world!
    <xhtml:img alt=":-)" src="smile.png" />
  </xhtml:body>
</xhtml:html>Writing a simple documentThe following example creates a very simple XHTML document.To make it simple, the output goes to aBytesIO, but you could also use
a binary file that has been created usingio.open(filename, "wb").>>> from __future__ import unicode_literals
>>> import io
>>> out = io.BytesIO()First create anXmlWriterto write the XML code to the specified output:>>> xml = XmlWriter(out)This automatically adds the XML prolog:>>> print out.getvalue().rstrip("\r\n")
<?xml version="1.0" encoding="utf-8"?>Next add the<html>start tag:>>> xml.startTag("html")Now comes the <body>. To pass attributes, specify them in a dictionary.
So in order to add:<body id="top">use:>>> xml.startTag("body", {"id": "top"})Let’ add a little text so there is something to look at:>>> xml.text("Hello world!")Wrap it up: close all elements and the document.>>> xml.endTag()
>>> xml.endTag()
>>> xml.close()And this is what we get:>>> print out.getvalue().rstrip("\r\n")
<?xml version="1.0" encoding="utf-8"?>
<html>
  <body id="top">
    Hello world!
  </body>
</html>Specifying attributesFirst create a writer:>>> import io
>>> out = io.BytesIO()
>>> xml = XmlWriter(out)Now write the content:>>> xml.tag("img", {"src": "smile.png", "alt": ":-)"})Attribute values do not have to be strings, other types will be converted to
Unicode using Python’sunicode()function:>>> xml.tag("img", {"src": "wink.png", "alt": ";-)", "width": 32, "height": 24})And the result is:>>> print out.getvalue().rstrip("\r\n")
<?xml version="1.0" encoding="utf-8"?>
<img alt=":-)" src="smile.png" />
<img alt=";-)" height="24" src="wink.png" width="32" />Using namespacesNow the same thing but with a namespace. First create the prolog
and header like above:>>> out = io.BytesIO()
>>> xml = XmlWriter(out)Next add the namespace:>>> xml.addNamespace("xhtml", "http://www.w3.org/1999/xhtml")Now elements can use qualified tag names using a colon (:) to separate
namespace and tag name:>>> xml.startTag("xhtml:html")
>>> xml.startTag("xhtml:body")
>>> xml.text("Hello world!")
>>> xml.endTag()
>>> xml.endTag()
>>> xml.close()As a result, tag names are now prefixed with “xhtml:”:>>> print out.getvalue().rstrip("\r\n")
<?xml version="1.0" encoding="utf-8"?>
<xhtml:html xmlns:xhtml="http://www.w3.org/1999/xhtml">
  <xhtml:body>
    Hello world!
  </xhtml:body>
</xhtml:html>Working with non ASCII charactersSometimes you want to use characters outside the ASCII range, for example
German Umlauts, the Euro symbol or Japanese Kanji. The easiest and performance
wise best way is to use Unicode strings. For example:>>> import io
>>> out = io.BytesIO()
>>> xml = XmlWriter(out, prolog=False)
>>> xml.text(u"The price is \u20ac 100") # Unicode of Euro symbol
>>> out.getvalue().rstrip("\r\n")
'The price is \xe2\x82\xac 100'Notice the “u” before the string passed toXmlWriter.text(), it declares the
string to be a unicode string that can hold any character, even those that are
beyond the 8 bit range.Also notice that in the output the Euro symbol looks very different from the
input. This is because the output encoding is UTF-8 (the default), which
has the advantage of keeping all ASCII characters the same and turning any
characters with a code of 128 or more into a sequence of 8 bit bytes that
can easily fit into an output stream to a binary file orio.BytesIO.If you have to stick to classic 8 bit string parameters, loxun attempts to
convert them to unicode. By default it assumes ASCII encoding, which does
not work out as soon as you use a character outside the ASCII range:>>> import io
>>> out = io.BytesIO()
>>> xml = XmlWriter(out, prolog=False)
>>> xml.text("The price is \xa4 100") # ISO-8859-15 code of Euro symbol
Traceback (most recent call last):
    ...
UnicodeDecodeError: 'ascii' codec can't decode byte 0xa4 in position 13: ordinal not in range(128)In this case you have to tell the writer the encoding you use by specifying
the thesourceEncoding:>>> import io
>>> out = io.BytesIO()
>>> xml = XmlWriter(out, prolog=False, sourceEncoding="iso-8859-15")Now everything works out again:>>> xml.text("The price is \xa4 100") # ISO-8859-15 code of Euro symbol
>>> out.getvalue().rstrip("\r\n")
'The price is \xe2\x82\xac 100'Of course in practice you will not mess around with hex codes to pass your
texts. Instead you just specify the source encoding using the mechanisms
described in PEP 263,Defining Python Source Code Encodings.Pretty printing and indentationBy default, loxun starts a new line for eachstartTagand indents the
content with two spaces. You can change the spaces to any number of spaces and
tabs you like:>>> out = io.BytesIO()
>>> xml = XmlWriter(out, indent="    ") # <-- Indent with 4 spaces.
>>> xml.startTag("html")
>>> xml.startTag("body")
>>> xml.text("Hello world!")
>>> xml.endTag()
>>> xml.endTag()
>>> xml.close()
>>> print out.getvalue().rstrip("\r\n")
<?xml version="1.0" encoding="utf-8"?>
<html>
    <body>
        Hello world!
    </body>
</html>You can disable pretty printing all together usingpretty=False, resulting
in an output of a single large line:>>> out = io.BytesIO()
>>> xml = XmlWriter(out, pretty=False) # <-- Disable pretty printing.
>>> xml.startTag("html")
>>> xml.startTag("body")
>>> xml.text("Hello world!")
>>> xml.endTag()
>>> xml.endTag()
>>> xml.close()
>>> print out.getvalue().rstrip("\r\n")
<?xml version="1.0" encoding="utf-8"?><html><body>Hello world!</body></html>Changing the XML prologWhen you create a writer, it automatically write an XML prolog
processing instruction to the output. This is what the default prolog
looks like:>>> import io
>>> out = io.BytesIO()
>>> xml = XmlWriter(out)
>>> print out.getvalue().rstrip("\r\n")
<?xml version="1.0" encoding="utf-8"?>You can change the version or encoding:>>> out = io.BytesIO()
>>> xml = XmlWriter(out, encoding=u"ascii", version=u"1.1")
>>> print out.getvalue().rstrip("\r\n")
<?xml version="1.1" encoding="ascii"?>To completely omit the prolog, set the parameterprolog=False:>>> out = io.BytesIO()
>>> xml = XmlWriter(out, prolog=False)
>>> out.getvalue()
''Adding other contentApart from text and tags, XML provides a few more things you can add to
documents. Here’s an example that shows how to do it with loxun.First, create a writer:>>> import io
>>> out = io.BytesIO()
>>> xml = XmlWriter(out)Let’s add a document type definition:>>> xml.raw("<!DOCTYPE html PUBLIC \"-//W3C//DTD XHTML 1.0 Strict//EN\" SYSTEM \"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd\">")
>>> xml.newline()Notice that loxun uses the genericXmlWriter.raw()for that, which allows to
add any content without validation or escaping. You can do all sorts of nasty
things withraw()that will result in invalid XML, but this is one of its
reasonable uses.Next, let’s add a comment:>>> xml.comment("Show case some rarely used XML constructs")Here is a processing instruction:>>> xml.processingInstruction("xml-stylesheet", "href=\"default.css\" type=\"text/css\"")And finally a CDATA section:>>> xml.cdata(">> this will not be parsed <<")And the result is:>>> print out.getvalue().rstrip("\r\n")
<?xml version="1.0" encoding="utf-8"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" SYSTEM "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<!-- Show case some rarely used XML constructs -->
<?xml-stylesheet href="default.css" type="text/css"?>
<![CDATA[>> this will not be parsed <<]]>OptimizationLoxun automatically optimized pairs of empty start/end tags. For example:>>> out = io.BytesIO()
>>> xml = XmlWriter(out)
>>> xml.startTag("customers")
>>> xml.startTag("person", {"id": "12345", "name": "Doe, John"})
>>> xml.endTag("person") # without optimization, this would add </person>.
>>> xml.endTag()
>>> xml.close()
>>> print out.getvalue().rstrip("\r\n")
<?xml version="1.0" encoding="utf-8"?>
<customers>
  <person id="12345" name="Doe, John" />
</customers>Despite the explicitstartTag("person")and matchingendtag(), the
output only contains a simple<person ... />tag.ContributingIf you want to help improve loxun, you can access the source code at
<http://github.com/roskakori/loxun>.FutureCurrently loxun does what it was built for.There are is no real plans to improve it in the near future, but here is a list
of features that might be added at some point:Add validation of tag and attribute names to ensure that all characters used
are allowed. For instance, currently loxun does not complain about a tag
named “a#b*c$d_”.Raise anXmlErrorwhen namespaces are added with attributes instead ofXmlWriter.addNamespace().Logging support to simplify debugging of the calling code. ProbablyXmlWriterwould get a propertyloggerwhich is a standardlogging.Logger. By default it could log original exceptions that
loxun turns into anXmlErrorand namespaces opened and closed.
Changing it tologging.DEBUGwould log each tag and XML construct
written, including additional information about the internal tag stack.
That way you could dynamically increase or decrease logging output.Rethink pretty printing. Instead of a global property that can only be set
when initializing anXmlWriter, it could be a optional parameter forXmlWriter.startTag()where it could be turned on and off as needed. And
the property could be namedliteralinstead ofpretty(with an
inverse logic).Add aDomWriterthat creates axml.dom.minidom.Document.Some features other XML libraries support but I never saw any real use for:Specify attribute order for tags.Version historyVersion 2.0, 2014-07-28Added support for Python 3.2+ while retaining the option to run with
Python 2.6+ (issue #5; thanks go toStefan Schwarzerwho offered his
guidance during a “Python 2 to 3” sprint at EuroPython 2014).Dropped support for Python 2.5, keep using loxun 1.3 if you are stuck
with with this version.Version 1.3, 2012-01-01AddedendTags()to close several or all open tags (issue #3,
contributed by Anton Kolechkin).AddedChainXmlWriterwhich is similar toXmlWriterand allows to
chain methods for more concise source code (issue #3, contributed by Anton
Kolechkin).Version 1.2, 2011-03-12FixedAttributeErrorwhenXmlWriter(...,encoding=...)was set.Version 1.1, 08-Jan-2011FixedAssertionErrorwhenprettywas set toFalse(issue #1; fixed by David Cramer).Version 1.0, 11-Oct-2010Added support for Python’swithso you don not have to manually callXmlWriter.close()anymore.Added Git repository at <http://github.com/roskakori/loxun>.Version 0.8, 11-Jul-2010Added possibility to pass attributes toXmlWriter.startTag()andXmlWriter.tag()with values that have other types thanstrorunicode. When written to XML, the value is converted using Python’s
built-inunicode()function.Added a couple of files missing from the distribution, most important the
test suite.Version 0.7, 03-Jul-2010Added optimization of matching start and end tag without any content in
between. For example,x.startTag("some");x.endTag()results in<some />instead of<some></some>.Fixed handling of unknown name spaces. They now raise anXmlErrorinsteadofValueError.Version 0.6, 03-Jun-2010Added optionindentto specify the indentation text each new line starts with.Added optionnewlineto specify how lines written should end.Fixed thatXmlWriter.tag()did not remove namespaces declared immediately
before it.Cleaned up documentation.Version 0.5, 25-May-2010Fixed typo in namespace attribute name.Fixed adding of namespaces before calls toXmlWriter.tag()which resulted
in anXmlError.Version 0.4, 21-May-2010Added optionsourceEncodingto simplify processing of classic strings.
The manual section “Working with non ASCII characters” explains how to use
it.Version 0.3, 17-May-2010Added scoped namespaces which are removed automatically byXmlWriter.endTag().Changedtext()to normalize newlines and white space if pretty printing
is enabled.Moved writing of XML prolog to the constructor and removedXmlWriter.prolog(). To omit the prolog, specifyprolog=Falsewhen
creating theXmlWriter. If you later want to write the prolog yourself,
useXmlWriter.processingInstruction().Renamed*Element()to*Tagbecause they really only write tags, not
whole elements.Version 0.2, 16-May-2010AddedXmlWriter.comment(),XmlWriter.cdata()andXmlWriter.processingInstruction()to write these specific XML constructs.Added indentation and automatic newline to text if pretty printing is
enabled.Removed newline from prolog in case pretty printing is disabled.Fixed missing “?” in prolog.Version 0.1, 15-May-2010Initial release.