Python Typing Module

The typing module provides type hints for function arguments, return values, and data structures.

from typing import TypedDict

Type hints do not change how Python runs your program. They help editors, linters, and readers understand what kinds of values your code expects.

Annotating function signatures

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

print(greet('Ada'))

Hello Ada

The annotation name: str means the function expects a string. The annotation -> str means it should return a string.

Common collection types

Use type hints to describe the shape of your data.

def average(values: list[float]) -> float:
    return sum(values) / len(values)

print(average([1.0, 2.0, 3.0]))

2.0

list[str] style annotations require Python 3.9+.

Optional values

Use | None when a value may be missing.

def find_user(user_id: int) -> str | None:
    if user_id == 1:
        return 'Ada'
    return None

print(find_user(1))
print(find_user(2))

Ada
None

The X | Y union syntax requires Python 3.10+.

TypedDict

TypedDict describes dictionary-like objects with fixed keys.

from typing import TypedDict

class User(TypedDict):
    name: str
    active: bool

user: User = {'name': 'Ada', 'active': True}
print(user['name'])

Ada

Type aliases

A type alias gives a readable name to a more complex type.

Coordinates = tuple[float, float]

def show_location(point: Coordinates) -> str:
    return f'{point[0]}, {point[1]}'

print(show_location((12.5, 35.8)))

12.5, 35.8