循环不破

Question

所以我有一个python程序有多个可能的输入，对于这一部分，我试图打破while循环，询问“输入产品成本”但是，当用户输入有效成本时，它只是重新加载他们输入另一个成本而不是结束。

while True:
    update_choice = input("What would you like to update? (c)ost or (q)uantity")
    if update_choice == "c":
    while True:
        new_price_update = float(input("Enter a product cost: "))
        if new_price_update > 0:
            for i in range(0, len(product_names)):
                if update_item == product_names[i]:
                    product_costs[i] = new_price_update
                    print("Product cost has been updated.")
                    break
                else:
                    print("Invalid price. Please try again.")

Answer 1

break仅退出当前循环。由于你打破了内部最多的循环，这只退出这个。你最后进入第二次循环。

Answer 2

while True:
        new_price_update = float(input("Enter a product cost: "))
        if new_price_update > 0:
            for i in range(0, len(product_names)):
                if update_item == product_names[i]:
                    product_costs[i] = new_price_update
                    print("Product cost has been updated.")
                break

您正在使用双循环语句： while True:和for i in range...。

break语句只会退出它所在的最里面的循环for循环，但会继续在while True:循环内循环，再次提示用户。

请改为尝试：

while True:
        new_price_update = float(input("Enter a product cost: "))
        if new_price_update > 0:
            for i in range(0, len(product_names)):
                if update_item == product_names[i]:
                    product_costs[i] = new_price_update
                    print("Product cost has been updated.")
                    break
            break

Answer 3

插入另一个break来停止内部while True:，因为break语句只会停止for语句，如下所示：

while True:
    update_choice = input("What would you like to update? (c)ost or (q)uantity")
    if update_choice == "c":
    while True:
        new_price_update = float(input("Enter a product cost: "))
        if new_price_update > 0:
            for i in range(0, len(product_names)):
                if update_item == product_names[i]:
                    product_costs[i] = new_price_update
                    print("Product cost has been updated.")
                    break
                else:
                    print("Invalid price. Please try again.")
            break

Answer 4

你的break只会'打破'内部for循环。为了突破第二个while循环，你需要将break放在for循环之外。

    while True:
        update_choice = input("What would you like to update? (c)ost or (q)uantity")
        if update_choice == "c":
            while True:
                new_price_update = float(input("Enter a product cost: "))
                if new_price_update > 0:
                    for i in range(0, len(product_names)):
                        if update_item == product_names[i]:
                            product_costs[i] = new_price_update
                            print("Product cost has been updated.")
                    break
                else:
                    print("Invalid price. Please try again.")

Answer 5

如果用户成功更新cost后，您想要打破整个过程，请尝试使用此代码：

# while loop (1)
while True:
    # flag to indicate updated successfully
    updated = False

    update_choice = input("What would you like to update? (c)ost or (q)uantity")

    if update_choice == "c":

        # while loop (2)
        while True:
            new_price_update = float(input("Enter a product cost: "))
            if new_price_update > 0:

                # for loop (1)
                for i in range(0, len(product_names)):
                    if update_item == product_names[i]:
                        product_costs[i] = new_price_update
                        print("Product cost has been updated.")

                        updated = True
                        # break out from for loop (1)
                        break
            else:
                print("Invalid price. Please try again.")

            if (updated == True):
                # break out from while loop (2)
                break

        if (updated == True):
            # break out from while loop (1)
            break