Flatten nested iterators of (nearly) arbitrary depth in Python 3.3+

flattener

def flattener(Xs):
    """flattener takes an object, Xs, which if iterable is recursively flattened
    yielding non-iterable objects, subject to any maximum recursion depth limits
    """
    if hasattr(Xs, "__iter__"):
        for x in Xs:
            yield from flattener(x)
    else:
        yield Xs