Python - type hints typing · Techiedeepdive

Python is, by design, dynamic typing language. which means you don’t have define types for variable. but that can be confusing for liners and IDE. This is from the offical docs

Note The Python runtime does not enforce function and variable type annotations. They can be used by third party tools such as type checkers, IDEs, linters, etc.

There are simple types that can be used to hint

>>> from typing import Dict, List, Tuple

>>> names: List[str] = ["Guido", "Jukka", "Ivan"]
>>> version: Tuple[int, int, int] = (3, 7, 1)
>>> options: Dict[str, bool] = {"centered": False, "capitalize": True}

There are more complicated things like Protocol which is used for type hints/checks for callable objects with __call__

from collections.abc import Iterable
from typing import Protocol

class Combiner(Protocol):
    def __call__(self, *vals: bytes, maxlen: int | None = None) -> list[bytes]: ...

def batch_proc(data: Iterable[bytes], cb_results: Combiner) -> bytes:
    for item in data:
        ...

def good_cb(*vals: bytes, maxlen: int | None = None) -> list[bytes]:
    ...
def bad_cb(*vals: bytes, maxitems: int | None) -> list[bytes]:
    ...

batch_proc([], good_cb)  # OK
batch_proc([], bad_cb)   # Error! Argument 2 has incompatible type because of
                         # different name and kind in the callback

Or Generic which used combined TypeVar for user-defined generics

KT = TypeVar('KT')
VT = TypeVar('VT')

class Mapping(Generic[KT, VT]):
    def __getitem__(self, key: KT) -> VT: