transpo.py

def main():
    myMessage = input('Text to cipher: ').upper()
    myKey = int(input('rail fence key: '))
    ciphertext = transpoMessage(myKey, myMessage)
    print(ciphertext)

def transpoMessage(key, plaintext):
    ciphertext = [''] * key
    for col in range(key):
        pointer = col
        while pointer < len(plaintext):
            ciphertext[col] += plaintext[pointer]
            pointer += key
    return ''.join(ciphertext)

if __name__ == '__main__':
    main()