python/simple-cipher/example.py

from string import ascii_lowercase
from time import time
import random


class Cipher:

    def __init__(self, key=None):
        if not key:
            random.seed(time())
            key = ''.join(random.choice(ascii_lowercase) for i in range(100))
        elif not key.isalpha() or not key.islower():
            raise ValueError('Wrong key parameter!')
        self.key = key

    def base_encode(self, s, shift):
        xkey = self.key * (len(s) // len(self.key) + 1)
        return ''.join(shift(c, k) for c, k in zip(s, xkey))

    def encode(self, s):
        s = _normalize(s)
        shift = lambda c, k: chr(((ord(c) + ord(k) - 2 * ord('a'))
                                  % len(ascii_lowercase)) + ord('a'))
        return self.base_encode(s, shift)

    def decode(self, s):
        shift = lambda c, k: chr(((ord(c) - ord(k) + len(ascii_lowercase))
                                  % len(ascii_lowercase)) + ord('a'))
        return self.base_encode(s, shift)


class Caesar(Cipher):

    def __init__(self):
        Cipher.__init__(self, 'd')


def _normalize(s):
    return ''.join([c for c in s if c.isalpha()]).lower()


if __name__ == '__main__':
    print(Caesar().encode('venividivici'))
    print(Caesar().encode('\'Twas the night before Christmas'))