def index_combinations():
    combs = [combinations_with_replacement(range(n_features), i) for i in range(0, (degree + 1))]
    flat_combs = [item for sublist in combs for item in sublist]
    return flat_combs
def index_combinations():
    combs = [combinations_with_replacement(range(n_features), i) for i in range(0, (degree + 1))]
    flat_combs = [item for sublist in combs for item in sublist]
    return flat_combs