Python2 and Python3 compatible carre de 25 encoder and decoder

25square.py

# -*- coding: utf-8 -*-
from __future__ import print_function
from six.moves import input, xrange, map
from string import ascii_letters

alphabet = "ABCDEFGHIJKLMNOPQRSTUVXYZ"


def get_maps(keyword):
    keyword = keyword.upper().replace('W', 'V')
    keyword = [c for c in keyword if c in ascii_letters]

    maps = []
    for c in keyword + list(alphabet):
        if c not in maps:
            maps.append(c)
    return maps


def show_maps(maps):
    for i in xrange(5):
        print('\n+---+---+---+---+---+')
        print('|', end='')
        for j in xrange(5):
            print(' %c |' % maps[i*5+j], end='')

    print('\n+---+---+---+---+---+\n')


class Encoder(object):
    def __init__(self, maps):
        self.maps = maps

    def encode(self, duo):
        if len(duo) < 2:
            return duo

        first_pos = self.maps.index(duo[0])
        second_pos = self.maps.index(duo[1])

        # Swap columns
        encoded_fpos = (int(first_pos / 5), second_pos % 5)
        encoded_spos = (int(second_pos / 5), first_pos % 5)

        # change the other coordinate if columns are both the same
        if first_pos % 5 == second_pos % 5:
            encoded_fpos = (int(second_pos / 5), first_pos % 5)
            encoded_spos = (int(first_pos / 5), second_pos % 5)

        # Get the encoded letter from coordinates
        encoded_duo = (self.maps[encoded_fpos[0] * 5 + encoded_fpos[1]],
                       self.maps[encoded_spos[0] * 5 + encoded_spos[1]])

        return encoded_duo


def transpose(text, maps):
    # Remove all whitespaces and capitalize
    text = text.upper().replace('W', 'V')
    text_ascii = [c for c in text if c in ascii_letters]

    # Build letter couples
    size = len(text_ascii)
    duos = [text_ascii[i:i+2] for i in range(0, size, 2)]

    # Generate for each duo its encoded_duo
    encoder = Encoder(maps)
    encoded_duos = map(encoder.encode, duos)

    return ''.join([''.join(x) for x in encoded_duos])


def main():
    keyword = input('Enter the keyword: ')

    maps = get_maps(keyword)

    assert len(maps) == 25

    show_maps(maps)

    text_to_transpose = input('Enter text:\n')

    print(transpose(text_to_transpose, maps))


if __name__ == '__main__':
    main()