See inline comments in code.
If you find this material initially too advanced, start where I did (video tutorials):
- [Derek Banas][http://www.newthinktank.com/2010/11/python-2-7-tutorial-pt-13-website-scraping/#comment-22377] ([@NewThinkTank][https://twitter.com/NewThinkTank]) Python 2.7 tutorials (13 parts, 2010)
- [Trevor Payne][https://www.youtube.com/playlist?list=PL82YdDfxhWsDJTq5f0Ae7M7yGcA26wevJ] YouTube video channel.