Python Typing Primer

Why Type Hints

Type hints are optional annotations that tools like mypy, Pyright, and your editor use to catch bugs before they hit production. They are ignored at runtime — zero performance penalty.

Basic Syntax

def greet(name: str) -> str:
    return f"Hello, {name}"

age: int = 42
scores: list[float] = [95.5, 88.0]

Common Types

• int, float, str, bool
• list[T], dict[K, V], tuple[T, ...]
• Optional[T] — shorthand T | None
• Union[A, B] — shorthand A | B
• Callable[[Args], Ret] for function signatures

TypedDict & Dataclasses

from typing import TypedDict

class User(TypedDict):
    id: int
    email: str
    verified: bool

Strict Mode

Add # pyright: strict at the top of a file to enforce full coverage. Run mypy --strict in CI to block untyped code from merging.