first thing first,Thank for the ebook from PACKTUB Artificial Intellegence with Python and Machine Learning with Python You must download the modul for machine learning(on code) and imporant thing you must install Python version 2.7 or 3.6 I suggest use Python 3.6 for updated module
i dont put the requirement.txt because i using only one module
Installing modul on python :
Windows :
pip install nltk
Ubuntu or Linux :
sudo pip install nltk
enjoy coding everyone