5 Best Ways to Disassemble Python Bytecode

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💡 Problem Formulation: Python developers often need to debug or analyze their compiled bytecode to understand what’s happening under the hood, optimize performance, or for educational purposes. The input for this task is Python bytecode, typically a .pyc file or equivalent in-memory bytecode, and the desired output is a readable disassembly that shows the Python virtual machine instructions.

Method 1: Using the dis Module

The dis module is included in Python’s standard library, offering a suite of functions for disassembling Python bytecode. It provides a readable interpretation of the bytecode and allows for disassembly of functions, methods, code strings, and code objects.

Here’s an example:

import dis

def greet():
    print("Hello, World!")

dis.dis(greet)

The output of this code will display the disassembled bytecode for the greet function, with opcodes and operands line by line.

This method of using the dis module is direct and does not require any additional libraries or tools. It’s a powerful means of understanding what the Python interpreter is doing with your code.

Method 2: Decompyle++

Decompyle++ is a Python decompiler that supports Python versions 2.5 through 2.7. It is capable of converting bytecode back to equivalent Python source code, which can provide insights into the implementation details of compiled Python files.

Here’s an example:

from decompyle3.main import decompile

compiled_file_path = 'compiled_file.pyc'
with open(compiled_file_path, 'rb') as f:
    decompile(2.7, f, sys.stdout)

The output will be the reconstructed source code from the given Python bytecode file.

While Decompyle++ is able to reconstruct the source code to a certain extent, it may not always produce perfectly readable code, especially when dealing with obfuscated or complex bytecode.

Method 3: pydevd

pydevd is both a debugger and a disassembler for Python that works within IDEs that support the PyDev plugin, such as Eclipse and Visual Studio Code. It allows developers to disassemble bytecode at breakpoints during debugging sessions.

Here’s an example:

import pydevd

pydevd.settrace()

def function_to_debug():
    a = 1
    b = 2
    return a + b

function_to_debug()

During the execution of the above snippet in a PyDev enabled environment, you can inspect the bytecode by setting a breakpoint.

pydevd is particularly useful for developers who prefer a graphical interface and who want to disassemble bytecode while debugging their programs interactively.

Method 4: xdis

xdis is an external Python library that extends the functionality of the dis module, providing disassembly for a broader range of Python bytecode versions.

Here’s an example:

from xdis import load

def example_func():
    return "Hello from xdis!"

bc = load.to_co(example_func.__code__)

import dis
dis.dis(bc)

The output again shows the detailed bytecode disassembly for the specified code object loaded by xdis.

xdis is especially useful if you’re dealing with multiple versions of Python and need a consistent interface to disassemble bytecode across them.

Bonus One-Liner Method 5: Use uncompyle6

uncompyle6 is a native Python decompiler that supports Python versions 2.7 and 3.x. It allows for one-liner disassembly of bytecode back into readable Python code.

Here’s an example:

!uncompyle6 -o . compiled_file.pyc

This command uses uncompyle6 to decompile the ‘compiled_file.pyc’ and outputs the result to the current directory.

This method is great for quick decompilations but keep in mind that for complex bytecode and certain Python versions, the output may not always be perfect.

Summary/Discussion

  • Method 1: The dis Module. Built into the Python standard library and easy to use. May not provide as many features as external tools, and it disassembles rather than decompiles.
  • Method 2: Decompyle++. Good for Python versions 2.5 to 2.7. May not decompile correctly if bytecode is obfuscated or complex.
  • Method 3: pydevd. Ideal for IDE users wanting to disassemble during debugging. Requires PyDev-compatible IDE and is better suited for interactive use than automation.
  • Method 4: xdis. Supports a wide range of Python versions. Requires external installation but is consistent across Python versions.
  • Bonus Method 5: uncompyle6. Convenient for quick decompilations with a one-liner command. The output may be less reliable with certain Python versions or obfuscated bytecode.