Type Hints — Optional but Powerful

Python 3.5+ supports optional type annotations. They don't enforce types at runtime but help IDEs, linters, and other developers.

Basic annotations:

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

def add(a: int, b: int) -> int:
    return a + b

def get_scores() -> list[int]:
    return [95, 87, 92]

Variables:

name: str = "Alice"
age: int = 30
scores: list[int] = [95, 87]
config: dict[str, str] = {}

Optional & Union:

from typing import Optional, Union

def find_user(id: int) -> Optional[str]:
    # returns str or None
    pass

def process(value: Union[int, str]) -> str:
    return str(value)

Type checking: Run mypy yourfile.py to catch type errors before runtime. Install: pip install mypy.

Why bother: Catches bugs early, improves autocomplete, makes code self-documenting.

Reference:

Wikipedia: Type System

https://en.wikipedia.org/wiki/Type_system