Else语句问题

Question

# Ceasar Cipher 


import pyperclip 

#this string to be encrypted/decrypted 
message = "this is my secret message" 

#the encryption/decryption key 
key = 13 

#Tells the program to encrypt or decrypt string 
mode = "Encrypt" 

#letters that can be encrypted 
LETTERS = "ABCDEFGHIJKLMNOPQRSTUVWXYZ" 

# stores the encrypted/decrypted form of the message 
translated = '' 

# capitalize the string in message 
message = message.upper() 

# run the encryption/decryption code on each symbol in the message string 
for symbol in message: 
     if symbol in LETTERS: 
      # get the encrypted (or decrypted) number for this symbol 
      num = LETTERS.find(symbol) # get the number of the symbol 
     if mode == 'encrypt': 
      num = num + key 
     elif mode == 'decrypt': 
      num = num - key 

     # handle the wrap-around if num is larger than the length of 
     # LETTERS or less than 0 
     if num >= len(LETTERS): 
      num = num - len(LETTERS) 
     elif num < 0: 
      num = num + len(LETTERS) 

     # add encrypted/decrypted number's symbol at the end of translated 
     translated = translated + LETTERS[num] 

     else: 
      translated = translated + symbol 

# print the encrypted/decrypted string to the screen 
print(translated) 

# copy the encrypted/decrypted string to the clipboard 
pyperclip.copy(translated) 

Answer 1

你不能声明

translated = translated + LETTERS[num] 

如果之间，ELIF和别人的。

另外，下一次，更清楚地说明你的问题。