Returns the other indicies in a list of length ``len_``

def index_complement(index_list, len_=None):
    """
    Returns the other indicies in a list of length ``len_``
    """
    mask1 = index_to_boolmask(index_list, len_)
    mask2 = not_list(mask1)
    index_list_bar = list_where(mask2)
    return index_list_bar