Building a Single-File Python Interpreter

Developer soasme is building small-python, a QuickJS-style single C11 source file implementation of the Python language core without the standard library, intended as a possible sandbox for agents to run untrusted code. The project has cost about $450 so far, mostly spent in one Claude Opus 5.5 session that ran for two days with the developer steering intermittently.

I’m working on a fun project: small-python https://github.com/soasme/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: 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.”