Beartype

Beartype is an open-source, pure-Python, PEP-compliant, near-real-time runtime-static type-checker. It emphasizes efficiency, portability, and readability, ensuring O(1) non-amortized worst-case runtime complexity with negligible constant factors. The library has no runtime dependencies and is actively maintained with frequent patch releases addressing compatibility and bug fixes, as evidenced by its rapid `0.22.x` release cycle.