Package: decompyle3
Contentsdecompyle3IntroductionWhy this?RequirementsInstallationRunning TestsUsageVerificationKnown Bugs/RestrictionsSee Alsodecompyle3A native Python cross-version decompiler and fragment decompiler.
A reworking ofuncompyle6.Introductiondecompyle3translates Python bytecode back into equivalent Python
source code. It accepts bytecodes from Python version 3.7 on.For decompilation of older Python bytecode seeuncompyle6.Why this?Uncompyle6 is awesome, but it has a fundamental problem in the way
it handles control flow. In the early days of Python when there was
little optimization and code was generated in a very template-oriented
way, figuring out control flow-structures could be done by simply looking at code patterns.Over the years more code optimization, specifically around handling
jumps has made it harder to support detecting control flow strictly
from code patterns. This was noticed as far back as Python 2.4 (2004)
but since this is a difficult problem, so far it hasn’t been tackled
in a satisfactory way.The initial attempt to fix to this problem was to add markers in the
instruction stream, initially this was aCOME_FROMinstruction, and
then use that in pattern detection.Over the years, I’ve extended that to be more specific, soCOME_FROM_LOOPandCOME_FROM_WITHwere added. And I added checks
at grammar-reduce time to make try to make sure jumps match with
supposedCOME_FROMtargets.However all of this is complicated, not robust, has greatly slowed
down deparsing and is not really tenable.So in this project we started rewriting and refactoring the grammar.However it is clear that even this isn’t enough. Control flow needs
to be addressed by using dominators and reverse-dominators which
thepython-control-flowproject can give.This I amfinallyslowly doing in yet another non-public project. It
is a lot of work.  Funding in the form of sponsorhip while greatly
appreciated isn’t commensurate with the amount of effort, and
currently I have a full-time job. So it may take time before it is
available publicly.RequirementsThe code here can be run on Python versions 3.7 or 3.8. The bytecode
files it can read have been tested on Python bytecodes from versions
3.7 and 3.8.InstallationYou can install from PyPI using the namedecompyle3:pip install decompyle3To install from source code, this project uses setup.py, so it follows the standard Python routine:$ pip install -e .  # set up to run from source treeor:$ python setup.py install # may need sudoA GNU Makefile is also provided somake install(possibly as root or
sudo) will do the steps above.Running Testsmake checkA GNU makefile has been added to smooth over setting running the right
command, and running tests from fastest to slowest.If you haveremakeinstalled, you can see the list of all tasks
including tests viaremake --tasksUsageRun$ decompyle3 *compiled-python-file-pyc-or-pyo*For usage help:$ decompyle3 -hVerificationIf you want Python syntax verification of the correctness of the
decompilation process, add the--syntax-verifyoption. However since
Python syntax changes, you should use this option if the bytecode is
the right bytecode for the Python interpreter that will be checking
the syntax.You can also cross compare the results with another python decompiler
likeunpyc37. Since they work differently, bugs here often aren’t in
that, and vice versa.There is an interesting class of these programs that is readily
available give stronger verification: those programs that when run
test themselves. Our test suite includes these.And Python comes with another a set of programs like this: its test
suite for the standard library. We have some code intest/stdlibto
facilitate this kind of checking too.Known Bugs/RestrictionsWe support only released versions, not candidate versions.Note however
that the magic of a released version is usually the same as thelastcandidate version prior to release.We also don’t handlePJOrionor otherwise obfuscated code. For
PJOrion try: PJOrionDeobfuscatorto unscramble the bytecode to get
valid bytecode before trying this tool;pydeciphermight help with that.This program can’t decompile Microsoft Windows EXE files created byPy2EXE, although we can probably decompile the code after you extract
the bytecode properly.Pydeinstallermay help with unpacking Pyinstaller bundlers.Handling pathologically long lists of expressions or statements is
slow. We don’t handleCythonor MicroPython which don’t use bytecode.There are numerous bugs in decompilation. And that’s true for every
other CPython decompiler I have encountered, even the ones that
claimed to be “perfect” on some particular version like 2.4.As Python progresses decompilation also gets harder because the
compilation is more sophisticated and the language itself is more
sophisticated. I suspect that attempts there will be fewer ad-hoc
attempts likeunpyc37(which is based on a 3.3 decompiler) simply
because it is harder to do so. The good news, at least from my
standpoint, is that I think I understand what’s needed to address the
problems in a more robust way. But right now until such time as
project is better funded, I do not intend to make any serious effort
to support Python versions 3.8 or 3.9, including bugs that might come
in. I imagine at some point I may be interested in it.You can easily find bugs by running the tests against the standard
test suite that Python uses to check itself. At any given time, there are
dozens of known problems that are pretty well isolated and that could
be solved if one were to put in the time to do so. The problem is that
there aren’t that many people who have been working on bug fixing.You may run across a bug, that you want to report. Please do so. But
be aware that it might not get my attention for a while. If you
sponsor or support the project in some way, I’ll prioritize your
issues above the queue of other things I might be doing instead.See Alsohttps://github.com/andrew-tavera/unpyc37/: indirect fork ofhttps://code.google.com/archive/p/unpyc3/The above projects use a different decompiling technique than what is used here. Instructions are walked. Some instructions use the stack to generate strings, while others don’t. Because control flow isn’t dealt with directly, it too suffers the same problems as the variousuncompyleanddecompyleprograms.https://github.com/rocky/python-xdis: Cross Python version disassemblerhttps://github.com/rocky/python-xasm: Cross Python version assemblerhttps://github.com/rocky/python-decompile3/wiki: Wiki Documents which describe the code and aspects of it in more detail