Untitled

#playfair cipher
def playfair(plaintext, key):
    #remove spaces and make all letters lowercase
    plaintext = plaintext.replace(' ', '')
    plaintext = plaintext.lower()
    key = key.replace(' ', '')
    key = key.lower()
    #remove duplicate letters from key
    key = ''.join(sorted(set(key), key=key.index))
    #remove j from key
    key = key.replace('j', '')
    #add key to matrix
    matrix = []
    for c in key:
        matrix.append(c)
    #add remaining letters to matrix
    for c in 'abcdefghiklmnopqrstuvwxyz':
        if c not in key:
            matrix.append(c)
    #print matrix
    print('Matrix:')
    for i in range(0, 25, 5):
        print(matrix[i:i+5])
    #add x between duplicate letters
    for i in range(0, len(plaintext)-1, 2):
        if plaintext[i] == plaintext[i+1]:
            plaintext = plaintext[:i+1] + 'x' + plaintext[i+1:]
    #add x to end if plaintext is odd length
    if len(plaintext) % 2 != 0:
        plaintext += 'x'
    #print plaintext
    print('Plaintext: %s' % plaintext)
    #encrypt plaintext
    ciphertext = ''
    for i in range(0, len(plaintext), 2):
        #find position of letters in matrix
        pos1 = matrix.index(plaintext[i])
        pos2 = matrix.index(plaintext[i+1])
        #find row and column of letters in matrix
        row1 = pos1 // 5
        col1 = pos1 % 5
        row2 = pos2 // 5
        col2 = pos2 % 5
        #encrypt letters
        if row1 == row2:
            ciphertext += matrix[row1*5 + (col1+1)%5]
            ciphertext += matrix[row2*5 + (col2+1)%5]
        elif col1 == col2:
            ciphertext += matrix[((row1+1)%5)*5 + col1]
            ciphertext += matrix[((row2+1)%5)*5 + col2]
        else:
            ciphertext += matrix[row1*5 + col2]
            ciphertext += matrix[row2*5 + col1]
    #print ciphertext
    print('Ciphertext:', ciphertext)
    return

#main
plaintext = 'Welcometomysecuritycourse'
key = 'PLAYFAIR'
playfair(plaintext, key)