Function 在Python3.4中创建Caesar密码程序，但函数不起作用

目前，我正在创建一个凯撒密码，但它不能正常工作，有人能帮忙吗？代码如下。目前，如果程序第一次运行（如中所示），则无需重新运行任何函数—它工作正常，但当重新运行getKey函数时，它会返回一个错误。代码后，错误显示为：

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()

我尝试在使用try、except和else命令的getKey函数期间创建它的防错功能。它将“尝试”查看输入是否为int，如果是，则转到else，但如果不是int，则将重新运行该函数。如果重新运行函数并输入int，则会出现以下错误：

这是it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 这是由于未输入int而必须重新运行getKey函数的示例：

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'

---

如您所见，它也会按照我的要求重新运行函数，但在将键添加到字符的ord时会出现错误。

第一次调用getKey时，请给出您的注释：

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

另一个你称之为的地方：

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

用户输入的内容来自getKey。。。你没有跟踪它，所以它消失了。那你就去吧

            return userKey

userKey仍然是您试图转换为int的H，即失败的H。你没有把它扔掉，所以它还在那里

更好的解决方案是修改代码的形状，这样getKey就不会在其内部调用getKey。在外部执行错误检查，例如这种形状：

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()

---

这段代码真的不需要这么复杂，如果你只使用正则表达式，代码会短得多，但在我看来更好

下面是我为Caesar cipher创建的一段代码，它可以加密、解密和使用用户选择的使用正则表达式的移位

import re

def caesar(plain_text, shift):
    cipherText = ''
    for ch in plain_text:
      stayInAlphabet = ord(ch) + shift
      if ch.islower():
        if stayInAlphabet > ord('z'):
          stayInAlphabet -= 26
        elif stayInAlphabet < ord('a'):
          stayInAlphabet += 26
      elif ch.isupper():
        if stayInAlphabet > ord('Z'):
          stayInAlphabet -= 26
        elif stayInAlphabet < ord('A'):
          stayInAlphabet += 26
      finalLetter = chr(stayInAlphabet)
      cipherText += finalLetter
    print(cipherText)
    return cipherText


selection = input ("encrypt/decrypt ")
if selection == 'encrypt':
  plainText = input("What is your plaintext? ")
  shift = (int(input("What is your shift? ")))%26
  caesar(plainText, shift)

else:
  plainText = input("What is your plaintext? ")
  shift = ((int(input("What is your shift? ")))%26)*-1
  caesar(plainText, shift)

---

将您的输入更改为原始输入

只需使用maketrans和translate函数，这些函数基本上可以为您加密或解密消息。它们可以为问题提供非常简短而有效的解决方案

message = input('enter message').lower()
offset = int(input('enter offset (enter a negative number to decrypt)'))
alphabet = 'abcdefghijklmnopqrstuvwxyz'
enc_alphabet = (alphabet[alphabet.index(alphabet[offset]):len(alphabet)])+ alphabet[0:offset]
data = str.maketrans(alphabet,enc_alphabet)
final_message = str.translate(message, data)
print(final_message)

---

我以前从未使用过return命令，因此从未意识到会发生这种情况。谢谢，它真的很有帮助，现在工作得很好！

message = input('enter message').lower()
offset = int(input('enter offset (enter a negative number to decrypt)'))
alphabet = 'abcdefghijklmnopqrstuvwxyz'
enc_alphabet = (alphabet[alphabet.index(alphabet[offset]):len(alphabet)])+ alphabet[0:offset]
data = str.maketrans(alphabet,enc_alphabet)
final_message = str.translate(message, data)
print(final_message)