说明：  Flask+Web开发实战的PDF版本。Flask是目前最流行的Python Web框架之一。自2010年开源以来，Flask受到了越来越多的Python开发者的喜欢，其受欢迎程度不输于Django。
(Flask+ PDF version of Web development practice. Flask is one of the most popular Python Web frameworks available today. Flask has been popular with more and more Python developers since open source in 2010 and is as popular as Django.)