Generics

Type variables let functions and classes work over any type while staying type-safe.

Intermediate

def first[T](items: list[T]) -> T:      # Python 3.12 syntax
    return items[0]

class Stack[T]:
    def __init__(self) -> None: self._items: list[T] = []
    def push(self, x: T) -> None: self._items.append(x)

Older code uses T = TypeVar("T") and Generic[T].

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