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Generics and Typing
Prerequisites: Functions
Python's type hints can describe a function that works generically
across types, while still being checked by tools like mypy before the
code even runs.
from typing import TypeVar
T = TypeVar("T")
def first_item(items: list[T]) -> T:
return items[0]
first_item([1, 2, 3]) # inferred as int
first_item(["a", "b", "c"]) # inferred as str
Type hints are never enforced by Python itself at runtime — they're
checked by a separate tool (mypy) as a way to catch mistakes before
running the code, not a hard runtime guarantee.