Package: trepan
AbstractFeaturesExact location informationDebugging Python bytecode (no source available)Source-code Syntax ColorizationCommand CompletionTerminal HandlingSmart EvalMore Stepping ControlStep GranularityDocumentationEvent Filtering and TracingEvent Tracing of Calls and ReturnsDebugger Macros via Python Lambda expressionsByte-code Instruction IntrospectionSome Debugger Command Arguments can be Variables and ExpressionsOut-of-Process DebuggingEgg, Wheel, and TarballsModularitySee AlsoAbstractThis is a gdb-like debugger for Python. It is a rewrite ofpdbfrom
the ground up.A command-line interface (CLI) is provided as well as an remote access
interface over TCP/IP.See theTutorialfor how to use. Seeipython-trepanfor using this
inipythonor anipython notebook.This package is for Python 3.2 and above. Seetrepan2for the same code
modified to work with Python 2.FeaturesSince this debugger is similar toothertrepanningdebuggersandgdbin general, knowledge gained by learning this is transferable to those
debuggers and vice versa.There’s a lot of cool stuff here that’s not in the stock
Python debuggerpdb.Exact location informationPython reports line information on the granularity of a line. To get
more precise information, we can (de)parse into Python the byte code
around a bytecode offset such as the place you are stopped at.So far as I know, there is no other debugger that can do this.Debugging Python bytecode (no source available)You can pass the debugger the name of Python bytecode and many times,
the debugger will merrily proceed.  This debugger tries very hard find
the source code. Either by using the current executable search path
(e.g.PATH) or for some by looking inside the bytecode for a
filename in the main code object (co_filename) and applying that
with a search path which takes into account directory where the
bytecode lives.Failing to find source code this way, and in other situations where
source code can’t be found, the debugger will decompile the bytecode
and use that for showing source test.This allows us to debug `eval`’d
or `exec’’d code.But if you happen to know where the source code is located, you can
associate a file source code with the current name listed in the
bytecode. See theset_substitutecommand for details here.Source-code Syntax ColorizationStarting with release 0.2.0, terminal source code is colorized viapygments. And with that you can set the pygments color style,
e.g. “colorful”, “paraiso-dark”. Seeset_style. Furthermore, we make use
of terminal bold and emphasized text in debugger output and help
text. Of course, you can also turn this off. Starting with release
0.6.0, you can use your ownpygments_style, provided you have a
terminal that supports 256 colors. If your terminal supports the basic
ANSI color sequences only, we support that too in both dark and light
themes.Command CompletionStarting with release 2.8, readline command completion has been
added. Command completion is not just a simple static list, but varies
depending on the context. For example, for frame-changing commands
which take optional numbers, on the list ofvalid numbersis
considered.Terminal HandlingWe can adjust debugger output depending on the line width of your
terminal. If it changes, or you want to adjust it, seeset_width.Smart EvalStarting with release 0.2.0, if you want to evaluate the current
source line before it is run in the code, useevalordeval. To evaluate text of a common fragment of line, such as the
expression part of anifstatement, you can do that witheval?ordeval?. Seeevalfor more information.More Stepping ControlSometimes you want small steps, and sometimes large stepping.This fundamental issue is handled in a couple ways:Step GranularityThere are nowstepeventandnexteventcommands with
aliases tos+,s>and so on. The plus-suffixed commands force
a different line on a subsequent stop, the dash-suffixed commands
don’t.  Suffixes>,<, and!specifycall,returnandexceptionevents respectively. And without a suffix you get
the default; this is set by theset differentcommand.DocumentationDocumentation:http://python3-trepan.readthedocs.orgEvent Filtering and TracingBy default the debugger stops at every event:call,return,line,exception,c-call,c-exception. If you just want
to stop atlineevents (which is largely what you happens inpdb) you can. If however you just want to stop at calls and returns,
that’s possible too. Or pick some combination.In conjunction with handlingallevents by default, the event status is shown when stopped. The reason for stopping is also available viainfo program.Event Tracing of Calls and ReturnsI’m not sure why this was not done before. Probably because of the
lack of the ability to set and move by different granularities,
tracing calls and returns lead to too many uninteresting stops (such
as at the same place you just were at). Also, stopping on function
definitions probably also added to this tedium.Because we’re really handling return events, we can show you the return value. (pdbhas an “undocumented”retvalcommand that doesn’t seem to work.)Debugger Macros via Python Lambda expressionsStarting with release 0.2.3, there are debugger macros.  Ingdb,
there is amacrodebugger command to extend debugger commands.However Python has its own rich programming language so it seems silly
to recreate the macro language that is ingdb. Simpler and more
powerful is just to use Python here. A debugger macro here is just a
lambda expression which returns a string or a list of strings. Each
string returned should be a debugger command.We also havealiasesfor the extremely simple situation where you
want to give an alias to an existing debugger command. But beware:
some commands, likestepinspect command suffixes and change their
behavior accordingly.We also envision a number of other ways to allow extension of this
debugger either through additional modules, or user-supplied debugger
command directories.If what you were looking for in macros was more front-end control over
the debugger, then consider using the experimental (and not finished)
Bullwinkle protocol.Byte-code Instruction IntrospectionWe do more in the way of looking at the byte codes to give better information. Through this we can provide:askipcommand. It is like thejumpcommand, but you don’t have to deal with line numbers.disassembly of code fragments. You can now disassemble relative to the stack frames you are currently stopped at.Better interpretation of where you are when insideexecfileorexec. (But really though this is probably a Python compiler misfeature.)Check that breakpoints are set only where they make sense.A more accurate determination of if you are at a function-definingdefstatement (because the caller instruction containsMAKE_FUNCTION.)Even without “deparsing” mentioned above, the abilty to disassemble by line number range or byte-offset range lets you tell exactly where you are and code is getting run.Some Debugger Command Arguments can be Variables and ExpressionsCommands that take integer arguments like frame-moving commands likeup, allow you to use a Python expression which may include local or
global variables that evaluates to an integer. This eliminates the
need ingdbfor special “dollar” debugger variables. (Note however
because ofshlexparsing, expressions can’t have embedded blanks.)Out-of-Process DebuggingYou can now debug your program in a different process or even a different computer on a different network!Egg, Wheel, and TarballsCan be installed via the usualpiporeasy_install. There is a
source tarball.How To Installhas
full instructions and installing from git and by other means.ModularityThe Debugger plays nice with other trace hooks. You can have several debugger objects.Many of the things listed below doesn’t directly effect end-users, but
it does eventually by way of more robust and featureful code. And
keeping developers happy is a good thing.(TM)Commands and subcommands are individual classes now, not methods in a class. This means they now have properties like the context in which they can be run, minimum abbreviation name or alias names. To add a new command you basically add a file in a directory.I/O is it’s own layer. This simplifies interactive readline behavior from reading commands over a TCP socket.An interface is it’s own layer. Local debugging, remote debugging, running debugger commands from a file (source) are different interfaces. This means, for example, that we are able to give better error reporting if a debugger command file has an error.There is an experimental Python-friendly interface for front-endsmore testable. Much more unit and functional tests. More ofpydb’s integration test will eventually be added.See Alsotrepan2: trepan debugger for Python 2pydbgr: previous incarnation of debuggerpydb: even older incarnation of debugger (for very old Python 2)Tutorial: Tutorial for how to usehttps://pypi.python.org/pypi/uncompyle6: Python decompilerhttps://pypi.python.org/pypi/xdis: cross-platform disassembler