為什么我一直收到此 python 錯誤 cost is not defined？

Question

我寫了這段代碼我得到一個錯誤說成本沒有定義

print("============================================================\n"
      "                 Welcome to Pizza Store                              \n"
      "============================================================\n")
def welcomescreen():
    print("1) Menu for the Pizza")
    print("2) Order the Pizza")
    print("3) Exit the program")
    ch = input("Select from one of the above: ")
    return ch
def main():
    choice = welcomescreen()
    while choice != '3':
            # based on user choice add appropriate method
        if choice == '1':
            print("1. Pepperoni               9 AED\n2. Margherita              12 AED\n3. Vegetarian              15 AED\n4. Neapolitan              21 AED")
            ask = input("Do you want to go back to the main menu? yes/no : \n").lower()
            if ask == "yes":
                main()
            elif ask == "no":
                break
        elif choice == '2':
            n=int(input("Enter the number of pizzas to be ordered: "))
            kind=input("Enter the kind of Pizza: ")
            size=input("Enter the size of Pizza\n(Large (50 AED),Medium (40 AED), Small (30 AED) : ")
            if(size == "Large"):
                cost_size=n*50
            elif(size == "Medium"):
                cost_size=n*40
            elif(size == "Small"):
                cost_size = n*30
            if(kind == "Pepperoni"):
              cost= n*10
              pizza = 'Pepperoni'
            elif(kind== "Margherita" ):
                cost= n*15
                pizza = "Margherita"
            elif(kind == "Vegetarian" ):
                cost= n*20
                pizza = "Vegetarian"
            elif(kind== "Neapolitan"):
                cost= n*18
                pizza = "Neapolitan"
            d=input("Enter toppings: \n").split(" ")
            extra=0
            if(len(d)>3):
                 extra= n*3*(len(d)-3)
#final Bill
            print("---------------------Your BILL-----------------------\n")
            print("The Pizza kind :", kind)
            print("The size :", size)
            print("Number of pizzas :  x", n)
            print("Extra toppings :")
            for i in d:
                print(i,end=" ")
            print("\n")
            print("==========Breakdown of bill========== \n")
            print("Bill for pizza         : ", cost)
            print("Bill for size         : ",cost_size)
            print("Bill for extra toppings: ",extra)
            print("Total Bill             : ",cost+cost_size+extra)

        else:
            print("Invalid choice. Try again.")
        
        choice = welcomescreen()

    print("Thank you! Have a nice day :)")
main()
 

---

我得到的錯誤是：

================================================ ========== 歡迎來到披薩店

1. 披薩菜單
2. 訂購披薩
3. 從上述其中一項退出程序 Select： 2 輸入要訂購的比薩餅數量： 1 輸入比薩餅的種類：意大利辣香腸 輸入比薩餅的大小（大（50 迪拉姆）、中（40 迪拉姆）、小（30 迪拉姆） ): large Enter toppings: pepperoni ----------------------Your BILL-------------------- ---

披薩種類：意大利辣香腸尺寸：大披薩數量：x 1 額外配料：意大利辣香腸

==========賬單明細==========

Exception has occurred: UnboundLocalError
cannot access local variable 'cost' where it is not associated with a value
  File "C:\Users\mandoof1\Downloads\Pizza part A.py", line 57, in main
    print("Bill for pizza         : ", cost)
  File "C:\Users\mandoof1\Downloads\Pizza part A.py", line 68, in <module>
    main()

應該發生的是根據您的輸入計算成本並給您賬單

Answer 1

只有當kind是您在 if/elifs 中檢查的三個字符串之一時，才會定義cost 。 具體來說，我認為發生的事情是你輸入了“意大利辣香腸”，但你真的想輸入“意大利辣香腸”（注意大寫）

為了更普遍地處理這個問題，您可能想要：

1. .lower()輸入kind和你要檢查的內容，所以你不必擔心大寫
2. 在檢查種類時有一個else子句，這樣如果用戶輸入了意想不到的東西，你就會知道。
3. 對size輸入也重復這兩個修復。