pycdc/pycdas is a C++11 command-line toolchain for reverse engineering CPython bytecode. pycdc decompiles compiled .pyc files back into human-readable Python source; pycdas emits a detailed bytecode disassembly (with options like --show-caches and --pycode-extra). Version coverage spans Python 1.0 (1994) through 3.13, with the correct opcode semantics selected from the .pyc magic number at load time. The entry points are pycdc.cpp and pycdas.cpp, which are thin CLIs over the pycxx static library that owns marshal-format parsing (pyc_object.cpp, pyc_numeric.cpp, pyc_string.cpp, pyc_sequence.cpp), code-object extraction (pyc_code.cpp), and interpreter version detection (pyc_module.cpp). It also supports decompiling raw marshalled code objects via -c -v <version>. Decompilation loads the code object and interprets its bytecode on a virtual stack machine (FastStack with history snapshots) inside ASTree.cpp, reconstructing structured control flow (loops, try/except, comprehensions, with-blocks) and lowering it into an ASTNode tree for source emission. Opcode semantics are maintained as an X-macro include (bytecode_ops.inl) with explicit version ranges, and per-version opcode-name maps live in bytes/python_*_*.cpp. The module boundaries cleanly separate binary I/O (endian-aware PycBuffer/PycFile streams), object marshalling, disassembly, AST construction, and printing - although the decompiler core itself is a dense, version-conditional megafile. QA is the project's strongest asset. Roughly 200 .pyc fixtures spanning every Python major release (plus an xfail set for known-unfixed cases) are checked by tests/run_tests.py, which compares decompiler output to expected output as token streams rather than exact text - tolerating cosmetic whitespace differences while still catching semantic regressions. Linux and Windows CI run the suite, and scripts/pymultic, Dockerfile.pybuild, and a collection of Autoconf modernization patches make it possible to rebuild ancient CPython releases to regenerate those fixtures. Recent commits cover Python 3.13 opcode support, and the repository is actively maintained. Caveats: the 25-year version matrix forces heavily conditional decompilation logic, some mutable global state exists in ASTree, and unknown or future-modified opcodes degrade to partial output with an 'Unsupported opcode' warning. For its niche, it is the most complete open-source CPython decompiler available.