test.txt

import re


class Playfair():
    """The Playfair Cipher enciphers pairs of characters, the key consists of
    a keysquare 25 characters in length.
    More information about the algorithm can be
    found at http://www.practicalcryptography.com/ciphers/playfair-cipher/.
    :param key: The keysquare, as a 25 character string.
    :param newkey: The key to make an unique keysquare
    """
    def __init__(self, newkey, key='ABCDEFGHIKLMNOPQRSTUVWXYZ'):
        newkey = newkey.replace(' ', '').upper().replace('J', 'I')
        newkey = ''.join([newkey, key])
        self.newkey = (sorted(set(newkey), key=newkey.index))

    def remove_punctuation(self, text, filter='[^A-Z]'):
        return re.sub(filter, '', text.upper())

    def encipher_pair(self, a, b):
        if a == b:
            b = 'X'
        arow, acol = int(self.newkey.index(a) / 5), self.newkey.index(a) % 5
        brow, bcol = int(self.newkey.index(b) / 5), self.newkey.index(b) % 5
        if arow == brow:
            return self.newkey[arow * 5 +
                               (acol + 1) % 5] + self.newkey[brow * 5 +
                                                             (bcol + 1) % 5]
        elif acol == bcol:
            return self.newkey[((arow + 1) % 5) * 5 +
                               acol] + self.newkey[((brow + 1) % 5) * 5 + bcol]
        else:
            return self.newkey[arow * 5 + bcol] + self.newkey[brow * 5 + acol]

    def decipher_pair(self, a, b):
        assert a != b, ('two of the same letters occurred together, '
                        'illegal in playfair')
        arow, acol = int(self.newkey.index(a) / 5), self.newkey.index(a) % 5
        brow, bcol = int(self.newkey.index(b) / 5), self.newkey.index(b) % 5
        if arow == brow:
            return self.newkey[arow * 5 +
                               (acol - 1) % 5] + self.newkey[brow * 5 +
                                                             (bcol - 1) % 5]
        elif acol == bcol:
            return self.newkey[((arow - 1) % 5) * 5 +
                               acol] + self.newkey[((brow - 1) % 5) * 5 + bcol]
        else:
            return self.newkey[arow * 5 + bcol] + self.newkey[brow * 5 + acol]

    def encipher(self, string):
        """Encipher string using Playfair cipher according to initialised key.
        Punctuation and whitespace
        are removed from the input. If the input plaintext is not an even
        number of characters, an 'X' will be appended.
        :param string: The string to encipher.
        :returns: The enciphered string.
        """
        string = self.remove_punctuation(string)
        string = re.sub(r'[J]', 'I', string)
        if len(string) % 2 == 1:
            string += 'X'
        ret = ''
        for c in range(0, len(string), 2):
            ret += self.encipher_pair(string[c], string[c + 1])
        return ret

    def decipher(self, string):
        """Decipher string using Playfair cipher according to initialised key.
        Punctuation and whitespace
        are removed from the input. The ciphertext should be an even number of
        characters. If the input ciphertext is not an even number of
        characters, an 'X' will be appended.
        :param string: The string to decipher.
        :returns: The deciphered string.
        """
        string = self.remove_punctuation(string)
        if len(string) % 2 == 1:
            string += 'X'
        ret = ''
        for c in range(0, len(string), 2):
            ret += self.decipher_pair(string[c], string[c + 1])
        return ret

if __name__ == '__main__':
    while True:
        print("Would you like to encode or decode")
        print("press [E] to encode, [D] to decode")
        inputselect = input("Pick an option between E and D:")
        if inputselect.lower() not in ('e', 'd'):
            print("Not an appropriate choice.")
        else:
            break

    if inputselect == 'e':
        print("")
        keyword = input('Enter a keyword: ')
        message = input('Enter string to encode: ')
        playfair_object = Playfair(keyword)
        print(playfair_object.encipher(message))

    if inputselect == 'd':
        print("")
        keyword = input('Enter a keyword: ')
        message = input('Enter string to decode: ')
        playfair_object = Playfair(keyword)
        print(playfair_object.decipher(message))