如何使python程序循環回到特定行

Question

我有以下代碼，如果發生某種偶然性，我希望它跳回到一行：

number_of_10ct = int(input("How many 10 Cent coins would you like to insert? "))
while number_of_10ct < 0:
    number_of_10ct = int(input("Please enter a positive number."))
number_of_20ct = int(input("How many 20 Cent coins would you like to insert? "))
while number_of_20ct < 0:
    number_of_20ct = int(input("Please enter a positive number."))
number_of_50ct = int(input("How many 50 Cent coins would you like to insert? "))
while number_of_50ct < 0:
    number_of_50ct = int(input("Please enter a positive number."))
number_of_100ct = int(input("How many 1 Rand coins would you like to insert? "))
while number_of_100ct < 0:
    number_of_100ct = int(input("Please enter a positive number."))
number_of_200ct = int(input("How many 2 Rand coins would you like to insert? "))
while number_of_200ct < 0:
    number_of_200ct = int(input("Please enter a positive number."))

number_of_500ct = int(input("How many 5 Rand coins would you like to insert? "))
while number_of_500ct < 0:
    number_of_500ct = int(input("Please enter a positive number."))

# Creating a variable to store the total amount of
# money inserted into the vending machine.
change = round(((number_of_10ct * 0.10) +
                (number_of_20ct * 0.20) + 
                (number_of_50ct * 0.50) + 
                (number_of_100ct * 1.00) +
                (number_of_200ct * 2.00) +
                (number_of_500ct * 5.00)),
               2)
# Informing the user how much they have entered in total.
print("\n")
print ('You have a credit of' ,change, 'ZAR')

while change > 0:
    customer_choice = input(("What would you like to buy?"
                             "Type N when you are finished \n"))
    if (customer_choice == "Kleiner Brauner" or
        customer_choice == "kleiner brauner" and
        change >= product_1_price):
        print ("You have chosen a", product_1,
               "these cost", product_1_price, "each,")
        change = round((change - product_1_price),2)
        print ("You have this much money remaining: R", change)
    elif (customer_choice == "Kakao" or
          customer_choice == "kakao" and
          change >= product_2_price):
        print ("You have chosen a", product_2,
               "these cost", product_2_price, "each,")
        change = round((change - product_2_price),2)
        print ("You have this much money remaining: R", change)
    elif customer_choice == "N" or customer_choice == "n":
        break
    elif change <= 0:
        print ("You have run out of money.")
        break
    else:
        print ("There has been an error or you may not have enough credit.")

我想發生的是：如果change = round((change - product_1_price),2)最終為負，那么我希望程序返回頂部（ number_of_10ct = int(input("How many 10 Cent coins would you like to insert? ")) ），並允許用戶輸入更多的“金錢”。

我怎樣才能做到這一點？

Answer 1

您可以做的是將所有代碼放入一個額外的while循環中，該循環將一直運行，直到change變為肯定為止（因此，您需要在循環之前將change初始化為負值）。

change = -1

while change < 0:
    # All the rest of your code (re-indented to be under this while loop)

這樣，在將更改設置為良好值之后，您將進入while change > 0循環。 一旦change變為負數，您就可以退出循環並返回頂部，用戶可以在此處添加硬幣。

然后，如果客戶決定在使用所有零錢之前不買任何東西，那么change仍然是正數，並且while change < 0循環while change < 0 ，您將擺脫困境。

Answer 2

使用while循環和continue語句：

while True:
  dostuff()
  if goback():
    continue  # back to start of loop
  else:
    break     # code after the loop