Python Typing — Type Annotations

Type hints catch bugs before runtime, improve IDE autocomplete, and serve as documentation.

Basic Types¶

from typing import Optional def greet(name: str, times: int = 1) -> str: return f”Hello {name}! ” * times def find_user(user_id: int) -> Optional[dict]: … # May return None

Python Typing — Type Annotations¶

def process(data: str | None) -> list[int]: …

Generics and Protocol¶

from typing import TypeVar, Protocol T = TypeVar(‘T’) def first(items: list[T]) -> T: return items[0] class Renderable(Protocol): def render(self) -> str: … def display(item: Renderable) -> None: print(item.render())

mypy¶

pyproject.toml¶

[tool.mypy] strict = true warn_return_any = true

Run¶

mypy src/

Key Takeaway¶

Type hints everywhere + mypy –strict. Catches bugs before runtime, improves DX.