Accepts a dict of lists. Returns keys that have vals with no length

def dict_where_len0(dict_):
    """
    Accepts a dict of lists. Returns keys that have vals with no length
    """
    keys = np.array(dict_.keys())
    flags = np.array(list(map(len, dict_.values()))) == 0
    indices = np.where(flags)[0]
    return keys[indices]