Transposition Cipher returning wrong results - encryption

Question

This is the source code I got from https://inventwithpython.com/hacking
import math, pyperclip
def main():
myMessage = 'Cenoonommstmme oo snnio. s s c'
myKey = 8
plaintext = decryptMessage(myKey, myMessage)
print(plaintext + '|')
pyperclip.copy(plaintext)
def decryptMessage(key, message):
numOfColumns = math.ceil(len(message) / key)
numOfRows = key
numOfShadedBoxes = (numOfColumns * numOfRows) - len(message)
plaintext = [''] * int(numOfColumns)
col = 0
row = 0
for symbol in message:
plaintext[col] += symbol
col += 1
if (col == numOfColumns) or (col == numOfColumns - 1 and row >= numOfRows - numOfShadedBoxes):
col = 0
row += 1
return ''.join(plaintext)
if __name__ == '__main__':
main()
What this Should be returning is
Common sence is not so common.|
What im getting back is
Coosmosi seomteonos nnmm n. c|
I cant figure out where the code is failing to send back the phrase

Answer 1

The code is OK. The problem is that you're using the wrong version of Python. As the 'Installation' chapter of that website says:
Important Note! Be sure to install Python 3, and not Python 2. The
programs in this book use Python 3, and you’ll get errors if you try
to run them with Python 2. It is so important, I am adding a cartoon
penguin telling you to install Python 3 so that you do not miss this
message:
You are using Python 2 to run the program.
The result is incorrect because the program depends on a feature that behaves differently in Python 2 than in Python 3. Specifically, dividing two integers in Python 3 produces a floating-point result but in Python 2 it produces a rounded-down integer result. So this expression:
(len(message) / key)
produces 3.75 in Python 3 but produces 3 in Python 2, and therefore this expression:
math.ceil(len(message) / key)
produces 4 (3.75 rounded up is 4) in Python 3 but produces 3 (3 rounded up is 3) in Python 2. This means that your numOfColumns is incorrect and therefore the decryption procedure produces an incorrect result.
You can fix this specific issue by changing (len(message) / key) to (float(len(message)) / key) to force Python 2 to treat that calculation as a floating-point division that will give the desired 3.75 result. But the real solution is to switch to using Python 3, because these differences in behaviour between Python 3 and Python 2 are just going to keep causing trouble as you proceed through the rest of the book.