Python if 语句无法正常工作

Question

为了澄清，我已经粘贴了我的整个程序，因为只有在我的程序中的所有代码出现问题时才能识别问题。我的问题是，我在我的程序中输入了 if else 和 elif 语句。当用户输入“否”时，程序结束，并且运行良好，如果用户输入“是”，则程序按预期进行。问题是当用户输入一些无效的内容时，除了“是”或“否”之外，它应该让他们重新输入他们的选项，但它会继续进行，就好像用户输入了“是”一样。

while True:
    print (" Position Finder")
    choice = (input("Do you want to run the Position Finder program? Please enter yes or no!"))
    # Lets the user input an answer to question I am asking it
    if choice.lower() == "no":
        # If the user input is "no" 
        print("The program will not run")
        # This statement will be printed out and the program will not run
        quit()
    elif choice.lower() == "yes":
        # If the user input is "yes"
        print("The program will now run")
    # This statement will be printed and the program will run
    else:
        # If an invalid statement is inputted
        print("Invalid entry, please type again")

    # This statement will be printed and the user will be given the option to input again


    sentList = "ask not what your country can do for you ask what you can do for your country"
    # Creates a list
    sentList2 = sentList.split()
    # This will split the list and give each word a position
    print (sentList)
    # This will print out the sentence in the program 

    word = (input("Enter Word: "))
    # Lets the user input a word from the sentence
    wordFound = False
    # This boolean statement, "wordFound" will be set to true when the word has been found in the list
    for (num, x) in enumerate(list(sentList2)):
        # For every word in the users sentence
        while word.lower() == x:
            # While the users word is equal to the position in the sentence
            print  (ordinalSuffix())
            # Print the ordinal suffix function
            wordFound = True
            # This boolean statement has been set to true as the word has been found in the list
            break
    # This will break the while loop from the boolean variable called "wordFound"


    if wordFound == False:
        # If the word has not been found in the list and the "wordFound" boolean variable has not been set to true
        print ("Please enter a word from the sentence")
        # This statement will print,meaning the user has to enter a word from the list

Answer 1

您可以使用continue 关键字。

continue 语句，也是从 C 中借来的，继续下一个 循环的迭代：

while True:
    print (" Position Finder")
    choice = (input("Do you want to run the Position Finder program? Please enter yes or no!"))
    if choice.lower() == "no":
        print("The program will not run")
        quit()
    elif choice.lower() == "yes":
        print("The program will now run")
    else:
        print("Invalid entry, please type again")
        continue  # move to next iteration
    rest_of_your_code()

Answer 2

您只在 else 子句中写了一条打印语句：print("Invalid entry, please type again")，但这不会使程序重复前面的指令。一个可能的解决方案：

choice = ""
while choice.lower() != "yes":
    choice = (input("Do you want to run the Position Finder program? Please enter yes or no!"))
    if choice.lower() == "no": 
            print("The program will not run")
            quit()
    elif choice.lower() == "yes":
            print("The program will now run")
    else:
            print("Invalid entry, please type again")

Answer 3

您需要为此添加一个while 循环，以语法错误的答案返回用户并在正确答案中中断循环。问题部分应如下所示：

while True:   # Main loop
    while True:   # Question loop
        choice = (input("Do you want to run the Position Finder program? Please enter yes or no!"))

        if choice.lower() == "no": 
            print("The program will not run")
            run = False
            break

        elif choice.lower() == "yes":
            print("The program will now run")
            run = True
            break

        else:
            print("Invalid entry, please type again")
            # In case of invalid entry Question loop will run again

    # Outside Question loop
    # Let's check if we should run the program
    if not run:
        break
        # This will be executed if *run* is False, it will break the Main loop

    # Your program