python-type-system

Type hints annotate function parameters and return values with expected types. Install mypy via pip, add type annotations to your code (e.g., `def greet(name: str) -> str:`), then run `mypy your_file.py` to detect type mismatches before runtime.

Type hints are static annotations that mypy analyzes without executing code, catching errors early. Python doesn't enforce type hints at runtime by default; mypy provides the checking layer that validates types match your annotations across modules.

TypedDict enforces a fixed structure and specific key types for dictionaries, enabling mypy to catch missing or incorrectly typed keys. Use it when you pass dictionaries between functions and need static verification of their shape and contents.

Configure mypy by creating a `mypy.ini` or adding `[tool.mypy]` section to `pyproject.toml` with settings like `strict = True` for strictness level, `ignore_missing_imports` for untyped dependencies, and `exclude` patterns. Run `mypy` to validate your entire project against these rules.

Protocols define structural interfaces without explicit inheritance—an object matches if it has the required methods and attributes. Use Protocols for flexible, type-safe APIs where you care about behavior, not class identity, enabling duck typing with static verification.

Yes, mypy supports PEP 604 union syntax (`int | str`) and built-in generic types (`list[int]`, `dict[str, int]`) in Python 3.10+. Configure mypy to recognize your Python version in `pyproject.toml` or `mypy.ini` to enable modern typing syntax validation.