Chapter 14 - Caesar Cipher

Chapter Content and Source Code

Download the source for cipher.py.

Or you can copy and paste the code from here:
# Caesar Cipher MAX_KEY_SIZE = 26 def getMode(): while True: print('Do you wish to encrypt or decrypt a message?') mode = input().lower() if mode in 'encrypt e decrypt d'.split(): return mode else: print('Enter either "encrypt" or "e" or "decrypt" or "d".') def getMessage(): print('Enter your message:') return input() def getKey(): key = 0 while True: print('Enter the key number (1-%s)' % (MAX_KEY_SIZE)) key = int(input()) if (key >= 1 and key <= MAX_KEY_SIZE): return key def getTranslatedMessage(mode, message, key): if mode[0] == 'd': key = -key translated = '' for symbol in message: if symbol.isalpha(): num = ord(symbol) num += key if symbol.isupper(): if num > ord('Z'): num -= 26 elif num < ord('A'): num += 26 elif symbol.islower(): if num > ord('z'): num -= 26 elif num < ord('a'): num += 26 translated += chr(num) else: translated += symbol return translated mode = getMode() message = getMessage() key = getKey() print('Your translated text is:') print(getTranslatedMessage(mode, message, key))

If you'd like to do the Caesar Cipher without the program, you can print and cut out this cipher wheel:

Download the PDF.

Online Diff Tool

If you've typed in the source code, but are seeing errors, you can compare your code to the book's code with the online diff tool.

Copyright © 2008, 2009, 2010 by Albert Sweigart
"Invent Your Own Computer Games with Python" 2nd Edition is free to copy and distribute under the Creative Commons Attribution-Noncommercial-Share Alike 3.0 United States License.