sources:
Web Scraping with Python by Ryan Mitchell, from page 109.
https://www.kaggle.com/rtatman/tutorial-getting-n-grams
https://www.nltk.org/ http://www.nltk.org/book/
books to look for: http://shop.oreilly.com/product/9780596516499.do http://shop.oreilly.com/product/0636920020578.do