Python Typing - Type Hints & Annotations

type-check.py

# static code analysis (mypy)
# mypy main.py [check miss match]
from typing import List, Dict, Set, Optional, Any, Sequence, TypeVar

def add_numbers(a: int, b: int, c: int) -> None:
  print(a + b + c)

add_numbers(1, 2, 3)

x: List[List[int]] = [[1, 2, 3], [1, 2, 3]] # nested list
x: Dict[str, str] = {"a", "b"}
x: Set[str] = {"a", "b"}

Vector = List[float]
def foo(v: Vector) -> Vector:
  return v
foo()

# Optional
def foo(output: Optional[bool]=False):
  pass
foo()

# Sequence: anything that can be indexed str, list, typle
def foo(seq: Sequence[str]):
  pass

# generic
T = TypeVar('T')
def get_item(lst: List[T], index: int) -> T:
  return lst[index]