How to Get the Most Out of the Python Decompilers Uncompyle6 and Decompyle3 - How to Write and Read

Python decompilers work differently from general-purpose decompilers like IDA Pro or Ghidra, as they are specifically designed for high-level bytecode rather than machine code

High-level bytecode decompilation is attractive for malware analysis because bytecode is portable, compact, and resistant to standard analysis tools

The decompilation process involves multiple phases:

• Disassembly of bytecode into instructions
• Tokenization of the disassembly
• Parsing tokens into a parse tree
• Converting parse tree to abstract syntax tree
• Generating source code from the AST

Python bytecode varies significantly between versions, making decompilation increasingly difficult with each new Python release

Uncompyle6 and Decompyle3 use grammar-based approaches to reconstruct source code, which helps handle nested control flow structures effectively

Control flow in Python bytecode decompilation is tied to specific Python versions and requires understanding concepts like dominator regions and basic blocks

Comments and formatting from original source code don’t appear in bytecode, making perfect reconstruction impossible

Current limitations include:

• Version-specific compatibility
• Difficulty handling newer Python versions
• Increasing complexity of Python bytecode
• Limited availability of tools for newer versions

Grammar-based decompilation produces more accurate results compared to pattern-matching approaches used by some other decompilers

Understanding bytecode structure and decompilation principles is crucial for analyzing malware written in Python, especially when source code is unavailable