ceaser cipher | Python Fiddle

#ceasar cipher
import pyperclip

#the string to be encrypted or decrypted
message = 'this is my secret message.'

#the encryption or decryption key
key = 13

#tells the program to decrypt or encrypt
mode = 'encrypt' #set to encrypt or decrypt

#every possible symbol that can be encrypted
LETTERS = 'ABCDEFGHIJkLMNOPQRSTUVWXYZ'

#stores the enc/dec for of the message
translated = ''

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

#run the enc/dec code on each symbol in the message string
for symbol in message:
    if symbol in LETTERS:
        #get the enc/dec 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 enc/dec numbers symbol at the end of the translated
        translated = translated + LETTERS[num]
        
    else:
        #just add the symbol without enc/dec it
        translated = translated + symbol
        
print(translated)

pyperclip.copy(translated)

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