Hi,
your demo Code - as shown in chapter 8 - which access yahoos historic data fails.
The failure is "yahoo_finance.YQLResponseMalformedError: Response malformed." after calling:
prices = get_prices('MSFT', '1992-07-22', '2016-07-22')
This "failure" is written in many articles, like:
http://www.financial-hacker.com/bye-yahoo-and-thank-you-for-the-fish/#more-2443