python-uncompyle6/README.rst

|buildstatus|

uncompyle6
==========

A native Python cross-version decompiler and fragment decompiler.
The successor to decompyle, uncompyle, and uncompyle2.


Introduction
------------

*uncompyle6* translates Python bytecode back into equivalent Python
source code. It accepts bytecodes from Python version 1.5, and 2.1 to
3.7 or so, including PyPy bytecode and Dropbox's Python 2.5 bytecode.

Why this?
---------

Ok, I'll say it: this software is amazing. It is more than your
normal hacky decompiler. Using compiler_ technology, the program
creates a parse tree of the program from the instructions; nodes at
the upper levels that look a little like what might come from a Python
AST. So we can really classify and understand what's going on in
sections of Python bytecode.

Building on this, another thing that makes this different from other
CPython bytecode decompilers is the ability to deparse just
*fragments* of source code and give source-code information around a
given bytecode offset.

I use the tree fragments to deparse fragments of code inside my
trepan_ debuggers_. For that, bytecode offsets are recorded and
associated with fragments of the source code. This purpose, although
compatible with the original intention, is yet a little bit different.
See this_ for more information.

Python fragment deparsing given an instruction offset is useful in
showing stack traces and can be encorporated into any program that
wants to show a location in more detail than just a line number at
runtime.  This code can be also used when source-code information does
not exist and there is just bytecode. Again, my debuggers make use of
this.

There were (and still are) a number of decompyle, uncompyle,
uncompyle2, uncompyle3 forks around. Almost all of them come basically
from the same code base, and (almost?) all of them are no longer
actively maintained. One was really good at decompiling Python 1.5-2.3
or so, another really good at Python 2.7, but that only. Another
handles Python 3.2 only; another patched that and handled only 3.3.
You get the idea. This code pulls all of these forks together and
*moves forward*. There is some serious refactoring and cleanup in this
code base over those old forks.

This demonstrably does the best in decompiling Python across all
Python versions. And even where there another project only provides
decompilation for subset of Python versions, we generally do
demonstrably better for those as well.

How can we tell? By taking the set of Python bytecode that comes
distributed with that version of Python, decompiling those and see how
many decompile properly; among that decompile, then make sure the
programs are syntactically correct, and in cases where the program can
be check with a provided test case, do that.

We are serious about testing, and use automated processes to find
bugs. In the issue trackers for other decompilers, you will find a
number of bugs we've found along the way. Very few to none of them are
fixed in the other decompilers.

Requirements
------------

The code here can be run on Python versions 2.6 or later, PyPy 3-2.4,
or PyPy-5.0.1.  Python versions 2.4-2.7 are supported in the
python-2.4 branch.  The bytecode files it can read have been tested on
Python bytecodes from versions 1.5, 2.1-2.7, and 3.0-3.6 and the
above-mentioned PyPy versions.

Installation
------------

This uses setup.py, so it follows the standard Python routine:

::

    pip install -e .  # set up to run from source tree
                      # Or if you want to install instead
    python setup.py install # may need sudo

A GNU makefile is also provided so :code:`make install` (possibly as root or
sudo) will do the steps above.

Testing
-------

::

   make check

A GNU makefile has been added to smooth over setting running the right
command, and running tests from fastest to slowest.

If you have remake_ installed, you can see the list of all tasks
including tests via :code:`remake --tasks`


Usage
-----

Run

::

$ uncompyle6 *compiled-python-file-pyc-or-pyo*

For usage help:

::

   $ uncompyle6 -h

If you want strong verification of the correctness of the
decompilation process, add the `--verify` option. But there are
situations where this will indicate a failure, although the generated
program is semantically equivalent. Using option `--weak-verify` will
tell you if there is something definitely wrong. Generally, large
swaths of code are decompiled correctly, if not the entire program.

You can also cross compare the results with pycdc_ . Since they work
differently, bugs here often aren't in that, and vice versa.


Known Bugs/Restrictions
-----------------------

The biggest known and possibly fixable (but hard) problem has to do
with handling control flow. (Python has probably the most diverse and
screwy set of compound statements I've ever seen; there
are "else" clauses on loops and try blocks that I suspect many
programmers don't know about.)

All of the Python decompilers that I have looked at have problems
decompiling Python's control flow. In some cases we can detect an
erroneous decompilation and report that.

In older versions of Python it was possible to verify bytecode by
decompiling bytecode, and then compiling using the Python interpreter
for that bytecode version. Having done this the bytecode produced
could be compared with the original bytecode. However as Python's code
generation got better, this is no longer feasible.

There is a kind of *weak verification* that we use that doesn't check
bytecode for equivalence but does check to see if the resulting
decompiled source is a valid Python program by running the Python
interpreter. Because the Python language has changed so much, for best
results you should use the same Python version in checking as was used
in creating the bytecode.

There are however an interesting class of these programs that is
readily available give stronger verification: those programs that
when run check some computation, or even better themselves.

And already Python has a set of programs like this: the test suite
for the standard library that comes with Python. We have some
code in `test/stdlib` to facilitate this kind of checking.

Python support is strongest in Python 2 for 2.7 and drops off as you
get further away from that. Support is also probably pretty good for
python 2.3-2.4 since a lot of the goodness of early the version of the
decompiler from that era has been preserved (and Python compilation in
that era was minimal)

There is some work to do on the lower end Python versions which is
more difficult for us to handle since we don't have a Python
interpreter for versions 1.5, 1.6, and 2.0.

In the Python 3 series, Python support is is strongest around 3.4 or
3.3 and drops off as you move further away from those versions. Python
3.6 changes things drastically by using word codes rather than byte
codes. As a result, the jump offset field in a jump instruction
argument has been reduced. This makes the `EXTENDED_ARG` instructions
are now more prevalent in jump instruction; previously they had been
rare.  Perhaps to compensate for the additional `EXTENDED_ARG`
instructions, additional jump optimization has been added. So in sum
handling control flow by ad hoc means as is currently done is worse.

Also, between Python 3.5, 3.6 and 3.7 there have been major changes to the
`MAKE_FUNCTION` and `CALL_FUNCTION` instructions.

Currently not all Python magic numbers are supported. Specifically in
some versions of Python, notably Python 3.6, the magic number has
changes several times within a version. We support only the released
magic. There are also customized Python interpreters, notably Dropbox,
which use their own magic and encrypt bytcode. With the exception of
the Dropbox's old Python 2.5 interpreter this kind of thing is not
handled.

We also don't handle PJOrion_ obfuscated code. For that try: PJOrion
Deobfuscator_ to unscramble the bytecode to get valid bytecode before
trying this tool. This program can't decompile Microsoft Windows EXE
files created by Py2EXE_, although we can probably decompile the code
after you extract the bytecode properly. For situations like this, you
might want to consider a decompilation service like `Crazy Compilers
<http://www.crazy-compilers.com/decompyle/>`_.  Handling
pathologically long lists of expressions or statements is slow.


There is lots to do, so please dig in and help.

See Also
--------

* https://github.com/zrax/pycdc : supports all versions of Python and is written in C++. Support for Python 3 is a bit lacking though.
* https://code.google.com/archive/p/unpyc3/ : supports Python 3.2 only. The above projects use a different decompiling technique than what is used here.
* https://github.com/figment/unpyc3/ : fork of above, but supports Python 3.3 only. Includes some fixes like supporting function annotations
* The HISTORY_ file.
* `How to report a bug <https://github.com/rocky/python-uncompyle6/blob/master/HOW-TO-REPORT-A-BUG.md>`_
* https://github.com/rocky/python-xdis : Cross Python version disassembler
* https://github.com/rocky/python-xasm : Cross Python version assembler
* https://github.com/rocky/python-uncompyle6/wiki : Wiki Documents which describe the code and aspects of it in more detail


.. _trepan: https://pypi.python.org/pypi/trepan2
.. _compiler: https://pypi.python.org/pypi/spark_parser
.. _HISTORY: https://github.com/rocky/python-uncompyle6/blob/master/HISTORY.md
.. _debuggers: https://pypi.python.org/pypi/trepan3k
.. _remake: https://bashdb.sf.net/remake
.. _pycdc: https://github.com/zrax/pycdc
.. _this: https://github.com/rocky/python-uncompyle6/wiki/Deparsing-technology-and-its-use-in-exact-location-reporting
.. |buildstatus| image:: https://travis-ci.org/rocky/python-uncompyle6.svg
		 :target: https://travis-ci.org/rocky/python-uncompyle6
.. _PJOrion: http://www.koreanrandom.com/forum/topic/15280-pjorion-%D1%80%D0%B5%D0%B4%D0%B0%D0%BA%D1%82%D0%B8%D1%80%D0%BE%D0%B2%D0%B0%D0%BD%D0%B8%D0%B5-%D0%BA%D0%BE%D0%BC%D0%BF%D0%B8%D0%BB%D1%8F%D1%86%D0%B8%D1%8F-%D0%B4%D0%B5%D0%BA%D0%BE%D0%BC%D0%BF%D0%B8%D0%BB%D1%8F%D1%86%D0%B8%D1%8F-%D0%BE%D0%B1%D1%84
.. _Deobfuscator: https://github.com/extremecoders-re/PjOrion-Deobfuscator
.. _Py2EXE: https://en.wikipedia.org/wiki/Py2exe