在Python 3.4中创建凯撒密码程序，但函数不起作用

Question

目前，我正在创建一个凯撒密码，但它不能正常工作，有人可以帮助吗？代码将在下面。目前，如果程序是第一次运行（就像现在一样，不需要重新运行任何函数），它可以很好地工作，但是当getKey（）函数重新运行时，它会返回一个错误。代码后面显示错误：

def runProgram():
    def choice():
        userChoice = input("Do you wish to Encrypt of Decrypt? Enter E or D: ").lower()
        if userChoice == "e":
            return userChoice
        elif userChoice == "d":
            return userChoice
        else:
            print("Invalid Response. Please try again.")
            choice()

    def getMessage():
        userMessage = input("Enter your message: ")
        return userMessage

    def getKey():
        try:
            userKey = int(input("Enter a key number (1-26): "))
        except:
            print("Invalid Option. Please try again.")
            getKey()
        else:
            if userKey < 1 or userKey > 26:
                print("Invalid Option. Please try again.")
                getKey()
            else:
                return userKey

    def getTranslated(userChoice, message, key):
        translated = ""
        if userChoice == "e":
            for character in message:
                num = ord(character)
                num += key
                translated += chr(num)

                savedFile = open('Encrypted.txt', 'w')
                savedFile.write(translated)
            savedFile.close()
            return translated
        else:
            for character in message:
                num = ord(character)
                num -= key
                translated += chr(num)
            return translated

    userChoice = choice() #Runs function for encrypt/decrypt selection. Saves choice made.
    message = getMessage() #Run function for user to enter message. Saves message.
    key = getKey() #Runs function for user to select key. Saves key choice.
    translatedMessage = getTranslated(userChoice, message, key) #Runs function to translate message, using the choice, message and key variables)
    print("\nTranslation complete: " + translatedMessage)
runProgram()

我尝试在getKey（）函数中使用try、except和else命令创建错误证明。它将“尝试”查看输入是否是int值，如果是，则转到else,但如果不是int值，则重新运行函数。如果重新运行该函数，并且输入了int值，则给出以下错误：

这是它工作的一个例子：

Do you wish to Encrypt of Decrypt? Enter E or D: E

Enter your message: Hello
Enter a key number (1-26): 5

Translation complete: Mjqqt

Do you wish to Encrypt of Decrypt? Enter E or D: E

Enter your message: Hello
Enter a key number (1-26): H
Invalid Option. Please try again.
Enter a key number (1-26): 5

Traceback (most recent call last):

  File "C:\Python34\Encryptor2.py", line 54, in 
    runProgram()
  File "C:\Python34\Encryptor2.py", line 52, in runProgram
    translatedMessage = getTranslated(userChoice, message, key) #Runs function to translate message, using the choice, message and key variables)
  File "C:\Python34\Encryptor2.py", line 35, in getTranslated
    num += key

TypeError: unsupported operand type(s) for +=: 'int' and 'NoneType'

正如您所看到的，它也像我所希望的那样运行函数，但是在将键添加到字符的顺序时发生了错误。

Answer 1

第一次调用getKey()，并附上注释：

key = getKey() #Runs function for user to select key. Saves key choice.

另一个你称之为：

        if userKey < 1 or userKey > 26:
            print("Invalid Option. Please try again.")
            getKey()

如果你用同样的注释来写，它会是：

            getKey() #Runs function for user to select key. Doesn't save key choice.

            return userKey

def getKey():
    prompt user for key
    try to convert to int and return the int
    if it fails, return None as an indication that getting the key went wrong.

key = None  #set some wrong placeholder
while (key is None) or (key < 1) or (key > 26):
    key = getKey()