Building a Single-File Python Interpreter
I’m working on a fun project: small-python. Implement a QuickJS-like single C11 source file that can do the same for Python language core, no Lib included. This goal is ambitious and it could be used for agents to run untrusted code.
To make that happen, I cannot simply say “hey Claude, implement a QuickJS-like project but for Python.” Instead, a few constraints are needed:
- Well-written specification
- Fuzzy testing
- A test262-like test spec (like test262)
- TLA formal verification
- Unittest, lots ported from CPython or RustPython
I’ve burned about $450 so far. Mostly using one single Claude Opus 5.5 session. The agent has been running for two days, and I’m steering, playing with my son, or going to sleep in the middle. Typically one steering session can run for several hours as I often say “don’t stop until.”
To be fair, I peeked at the C code once. It’s pretty understandable—just like the C parser code I wrote over the years. Nothing magic, but it’s substantial already.