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Learn: Type hints

Four notebooks, in order. Each is self-contained but they build on each other — if you work through them in sequence you'll cover the whole topic once.

Notebooks in this section

  1. Why type hints? — what they are, what they aren't, and what problem they solve. How type-checkers use them.
  2. Basic annotations — annotating variables, function parameters, and return types. The built-in types (int, str, bool, etc.) and how they compose.
  3. Generics and collections — typing containers: list[int], dict[str, int], tuple[int, str], custom generics via TypeVar.
  4. Optional, Union, and friends — X | None, X | Y, Literal, Callable, TypedDict, Any and object. The expressive forms you'll reach for as your typing gets more ambitious.

After these, the Recipes show task-focused applications and the Reference has lookup tables for the typing module.