Mypyc Can Double Python Library Speed Without Leaving Python

A developer demonstrated how to nearly double the performance of h11, a widely used Python HTTP/1.1 library with 710,000 GitHub dependents, using mypyc instead of rewriting code in Rust. Mypyc is an ahead-of-time compiler that converts type-annotated Python code into native CPython C extensions, eliminating runtime interpretation overhead. It achieves speedups by using efficient data representations, resolving function calls at compile time, and reducing dynamic namespace lookups. The process involves three stages: satisfying mypy's strict type checks, successfully compiling with mypyc, and verifying the compiled code works correctly at runtime. The author also documented real annotation errors encountered during the migration, such as bytearray and bytes mismatches, and how each was resolved.