Intermediate Python is free on leanpub: For just tonight my first ebook on leanpub is free. If you do download it, endeavour to please leave some feedback. Link is https://leanpub.com/intermediatepython
It's not an intuitive interface, but it works -- use the slider to slide the price downward to zero. It's a variable-pricing model with varying payout to the author.
(I'm not criticizing the pricing model, I'm just saying the free-purchase method wasn't obvious to me, either, at first.)
I bet you'd get more ultimate conversions if you stated that full-price purchasers would be granted the full book upon completion (and correction/minor update versions as well).
Page 12: 'function definitioin'. Page 19: Opportunity for introducing 'with' statement. Page 28: 'Python doesnâ€TMt', amusingly in a paragraph discussing character encoding. Page 31: Broken table. Page 38: 'frame —'. Page 52: 'Hey I dont see' - opportunity for escaped apostrophe.