Miguel Grinberg's "Flask Web Development" [1] is an excellent introduction Python-based web development. You build a Twitter-clone. The book is an adaptation of the authors 18-part tutorial on the same topic [2].

[1] http://shop.oreilly.com/product/0636920031116.do

[2] https://blog.miguelgrinberg.com/post/the-flask-mega-tutorial...