Python - Transposition cipher

#
# https://www.facebook.com/groups/learnpython.org/permalink/1175691462495469/
#
# https://en.wikipedia.org/wiki/Transposition_cipher
#

import math # import at top of code to show users what modules they need to run it.


def transencrypt(word, key):

    result = ''

    length = len(word)

    for count1 in range(key):
        for count2 in range(count1, length, key):
            result += word[count2]

    return result


def transdecrypt(word, key):

    length = len(word)

    result = [''] * length

    pos = 0

    for count1 in range(key):
        for count2 in range(count1, length, key):
            result[count2] = word[pos]
            pos += 1

    return ''.join(result)

# encryption - almost identical to decryption - only one line is different

def transencrypt(word, key):

    length = len(word)

    result = [''] * length

    pos = 0

    for count1 in range(key):
        for count2 in range(count1, length, key):
            result[pos] = word[count2]  # different line
            pos += 1

    return ''.join(result)


# encryption - version with iterator

def transdecrypt_version2(word, key):

    length = len(word)

    result = [''] * length

    letter = iter(word) # iterator let you get next element/letter using next()

    for count1 in range(key):
        for count2 in range(count1, length, key):
            result[count2] = next(letter)

    return ''.join(result)


# --- almost "UnitTest" ;) ---

print('--- encryption ---')

print(transencrypt('', 5) == '')
print(transencrypt('bye', 5) == 'bye')
print(transencrypt('hello', 5) == 'hello')

print(transencrypt('hello world', 5) == 'h dewlolrol')

print('--- decryption ---')

print(transdecrypt('', 5) == '')
print(transdecrypt('bye', 5) == 'bye')
print(transdecrypt('hello', 5) == 'hello')

print(transdecrypt('h dewlolrol', 5) == 'hello world')

# --- or using `asssert` command ---

assert transencrypt('hello world', 5) == 'h dewlolrol', 'wrong encryption'
assert transdecrypt('h dewlolrol', 5) == 'hello world', 'wrong decryption'