Universal function to return unique items in iterable

unique_everseen.py

def unique_everseen(items: Iterable, get_hashable: Callable[[Any], Any]=None) -> Iterable:
    """
    Returns generator of unique items.
    If get_hashable(item) is not None or all elements hashable, fast method would be used.
    """
    if callable(get_hashable):
        seen = set()
        return (i for i in items for h in (get_hashable(i),) if not (h in seen or seen.add(h)))
    elif all(isinstance(i, collections.Hashable) for i in items):
        seen = set()
        return (i for i in items if not (i in seen or seen.add(i)))
    else:
        seen = list()
        return (i for i in items if not (i in seen or seen.append(i)))