Caesar Cipher

caesar.py

"""
Simple implementation of the Caesar cipher that works for the English alphabet
"""

alphabet = [chr(letter) for letter in range(97, 123)]

def caesar_cipher(text, key):
    """
    Enciphers/deciphers a text.
    @param text: to encipher/decipher
    @param key: use a positive number to encipher and a negative to decipher
    """
    text_ = ""
    for c in text:
        text_ += shift(c.lower(), key)
    return text_

def shift(char, n):
    """ Shifts a letter by `n` letters and wraps at z to a."""
    try:
        index = alphabet.index(char)
    except ValueError:
        return char  # unknown letter
    index += n
    if index > 25: index = index - 26
    return alphabet[index]


text = "Hello, my name is CasperCL"
code = caesar_cipher(text, 13)
deciphered = caesar_cipher(code, -13)
assert text.lower() == deciphered