如何在用户输入无法识别的答案时创建错误消息

Question

def program():
    print ('Start program')
    choice = input("please select either a card or coin?")

    if choice == "COIN":    
        print ("you will now be given heads or tails")
    elif choice == "Coin":
        print ("you will now be given heads or tails")
    elif choice == "coin":
        print ("you will now be given heads or tails")


    import random
    higher_value = 2
    lower_value = 1
    final_value = random.randint (lower_value, higher_value)
    if final_value == 1:
        print ("Heads")
    else:
        print ("Tails")
#~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
                                    #CARD
    if choice == "Card":
        print("you will now be given a number for; number,suit")
    elif choice == "card":
        print ("you will now be given a number for; number,suit")
    elif choice == "CARD":
        print ("you will now be given a number for; number,suit")

    import random
    higher_value = 13
    lower_value = 1
    final_value = random.randint (lower_value, higher_value)

    if final_value == 1:
               print ("ace")
    if final_value == 2:
               print ("2")
    if final_value == 3:
               print ("3")
    if final_value == 4:
               print ("4")
    if final_value == 5:
               print ("5")
    if final_value == 6:
               print ("6")
    if final_value == 7:
               print ("7")
    if final_value == 8:
               print ("8")
    if final_value == 9:
               print ("9")
    if final_value == 10:
               print ("10")  
    if final_value == 11:
               print ("Jack")
    if final_value == 12:
               print ("Queen")
    if final_value == 13:
               print ("King")

    import random
    higher_value = 4
    lower_value = 1
    final_value = random.randint (lower_value, higher_value)
    if final_value == 1:
               print ("Hearts")
    if final_value == 2:
               print ("Clubs")
    if final_value == 3:
               print ("Spades")
    if final_value == 4:
               print ("Diamonds")
#------------------------------------------------------------------------------------------------------------------------------
                                    #REPEAT LOOP
flag = True
while flag:
    program()
    flag = input('Would you like to run the program again? [y/n]') == 'y'
print ("The program will now terminate.")
print ("Have a good day")

我正在尝试解决当用户输入错误数据时如何出错，例如，如果用户输入某些内容而不是卡或硬币的两个选项。

会出现一条错误消息，然后要求用户重新输入数据，当用户输入卡或硬币时，它也会产生拾卡和抛硬币的结果我希望程序输出硬币或卡片

Answer 1

choice = choice.lower()
if choice == 'card':
    # do the card thing
elif choice == 'coin':
    # do the coin thing
else:
    # print an error message

Answer 2

若要回答有关在用户输入错误答案时显示错误的第一个问题，您需要在每次要求用户输入时循环：

choice = input("Please select either a card or coin: ").lower()
while choice not in ('card', 'coin'):
    choice = input("You did not enter a correct choice, please select either a card or coin: ").lower()

然后，如果他们建议将卡片或硬币包装在一个大的if语句中，则需要将完成工作的逻辑包装起来：

if choice == 'card':
    # card logic goes here
elif choice == 'coin':
    # coin logic goes here
else:
    # Shouldn't reach this (your while loop above should catch it)
    # But error anyway, just in case