from typing import TypeVar, Hashable, Callable, Set, Iterable, Iterator

T = TypeVar("T")
K = TypeVar("K", bound=Hashable)


def keyed_filter(iterable: Iterable[T], key: Callable[[T], K]) -> Iterator[T]:
    """Yields the iterable without key duplicates.

    >>> list(keyed_filter(["Alice","Adam","Bob","Ben"],key=lambda x:x[0]) )
    ['Alice', 'Bob']
    """
    seen_values: Set[K] = set()
    for val in (val for val in iterable if key(val) not in seen_values):
        seen_values.add(key(val))
        yield val