#type-checking

#type-checking

Python in 2025 is rapidly evolving: the GIL is being phased out, packaging and tooling are improving, and type checking and AI-related tooling are rapidly proliferating.

ty is a fast, pragmatic, ergonomic, open-source (MIT) type checker with Rust-inspired diagnostics and significantly faster incremental updates on large projects.

TypedDict now controls both key requiredness and whether extra keys are allowed, with Python 3.15 adding closed TypedDict behavior to restrict unknown keys.

TypeScript infers literal argument types causing compile-time errors for mismatched values; Python's mypy requires explicit annotations to report the same mismatches.

Lazy annotations in Python 3.14 defer evaluation of annotations to improve performance, fix forward reference issues, and support static type checking and runtime processing.