第27行的字符串索引超出范围

Question

我正试图用非复杂的代码做一个基本的Ceaser密码，当我键入类似Go Buy Bread的内容并将移位设置为8或更高时，我会得到一个错误，称为字符串索引超出范围，我不想使用mod(%(。有人能给我一个解决方案吗？

Alphabet = 'ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz1234567890 -!?.'

FinalMessage = ''

print("Cipher/Decipher Code")
print("-")
print("This code can encode messages and decode messages.")

while True:
print()
Option = int(input('Type the number 1 to encode your message, number 2 to decode, number 3 to exit: '))  
print()                                                                                                  
if Option == 1:  
Message = list(input("Type the message you want to encode: "))  
print()                                                         
print("To encode the message type a number between 1 and 26.")  
print("The number means how many letters the message will shift.")
Key = int(input("Number: "))  
for Cipher in Message:  
if Cipher in Alphabet:  
Position = Alphabet.find(Cipher) 
NewPosition = (Position + Key)
NewCipher = Alphabet[NewPosition]
FinalMessage += NewCipher  
else:  
FinalMessage += Cipher 
print()
print("Encrypted Message: " + FinalMessage) 
print()
print("------")
print()
elif Option == 2:
print()
Message = list(input("Type the message you want to decode: "))
print()
print("To decode a message type a number between 1 and 26.") 
print("The number means how many letters the message will shift")  
Key = int(input("Number: "))  
Key = (Key * -1) 
for Cipher in Message:  
if Cipher in Alphabet: 
Position = Alphabet.find(Cipher) 
NewPosition = (Position + Key)
NewCipher = Alphabet[NewPosition]
FinalMessage += NewCipher
else:  
FinalMessage += Cipher 
print()
print("Decrypted Message: " + FinalMessage) 
print()
print("------")
print()
FinalMessage = "" 

Answer 1

不确定为什么您不想使用%，这似乎是理想的选择。否则，您将不得不手动检查调整后的索引是否超出字母表的范围，并添加/减去字母表的大小以正确换行。

两种方法是：

# Method 1 (preferred).
NewPosition = (Position + Key) % len(Alphabet)
# Method 2 (ugly and unnecessary).
NewPosition = Position + Key
if NewPosition >= len(Alphabet):
NewPosition -= len(Alphabet)

然而，移位为(正(八的Go Buy Bread不会给alpha字符带来包装问题，因为所有结果都仍在字符串中。如果你减去八，可能会这样，但我假设你想对明文消息进行编码，而不是解码。

因此，您最好的选择是通过每次在循环中打印Position和NewPosition(以及len(Alphabet)(来开始调试。希望这能告诉你发生了什么。