python - 誰かがこのエラーを説明できますか - 「実行時エラー: 反復中に辞書サイズが変更されました」?

Question

def find_the_best_solution(shipping_request, list, current_solution, best_shipping_solution):
    if shipping_request == {}:
        return current_solution

    for item in shipping_request:
        for i in range(0,len(list), 1):
            length_of_combination = i+1
            combinations = itertools.combinations(list, length_of_combination)
            for x in combinations:
                if sum(x) >= shipping_request[item]:
                    if sum(x) > shipping_request[item]:
                        current_solution['wastage'] += (sum(x) - shipping_request[item])
                    current_solution['number_of_containers'] += length_of_combination
                    current_solution['distribution'][item] = x
                    temp_request = shipping_request
                    del temp_request[item]
                    temp_list = list
                    for y in x:
                        temp_list.remove(y)
                    solution = find_the_best_solution(temp_request, temp_list, current_solution, best_shipping_solution)
                    if solution['wastage'] < best_shipping_solution['wastage']:
                        best_shipping_solution = solution
                    elif solution['wastage'] == best_shipping_solution['wastage']:
                        if solution['number_of_containers'] < best_shipping_solution['number_of_containers']:
                            best_shipping_solution = solution

    return best_shipping_solution   

これにより、次のエラーが発生します-「実行時エラー: 反復中に辞書サイズが変更されました」

私は何を間違っていますか？どうすれば別の方法で行うことができますか？