Update, June 2017: The former books (a nested books/index.html) and training (the toplevel's training.html) sites have been merged into learning-python.com—a shared top-level folder that is the union of all other prior parts, also hosts programs and posts, and appeases search engines with HTTP URL redirects via custom Apache .htaccess rewrite rules. Engineers love to change things...
The domain name learning-python.com hosts two related but distinct websites:
Site History—the books site formerly resided at www.rmi.net/~lutz for some two decades, but was relocated due to quota limits imposed by a former ISP. You can read the story behind its October 2015 relocation at this page.
Browser Portability—these web sites have been tested successfully on Chrome, Firefox, Internet Explorer, Opera, and Safari, but Edge is not currently recommended due to its buggy URL popup behavior for lower-left links described on this page.