Tornado is obviously different from the current mainstream Web server frameworks (including most Python frameworks): it is a non-blocking server with quite fast speed. Due to its non-blocking mode and the use of epoll, Tornado can handle thousands of connections per second, which means that Tornado is an ideal Web framework for real-time Web services. The main purpose of developing this Web server is to handle the real-time function of FriendFeed-in the application of FriendFeed, every active user will maintain a server connection.
Flask is a lightweight Web application framework written in Python. Its WSGI toolbox uses Werkzeug, and its template engine uses Jinja2.
Flask uses BSD authorization.
Flask is also called "micro-frame" because it uses a simple core and uses extensions to add other functions. By default, Flask has no database and form validation tools. However, Flask retains the flexibility of extension, and Flask-extension can be used to add these functions: ORM, form verification tools, file uploading, and various open authentication technologies.