Flask is a micro framework. Micro refers to the small core of the framework, not the ability to create single-file applications. Flask basically provides routing and templating, wrapped around a few configuration conventions. Its objective is to be flexible and allow the user to pick the tools that are best for their project. It provides many hooks for customization and extensions.
Flask curiously started as an April Fool's joke, but it's in fact a very serious framework, heavily tested and extensively documented. It features integrated unit testing support and includes a development server with a powerful debugger that lets you examine values and step through the code using the browser.
Flask is unicode-based and supports the Jinja2 templating engine, which is one of the most popular for Python web applications. Though it can be used with other template systems, Flask takes advantage of Jinja2's unique features, so it's really not advisable to do so.
Flask's routing system is very well-suited for RESTful request dispatching, which is really a fancy name for allowing specific routes for specific HTTP verbs (methods). This is very useful for building APIs and web services.
Other Flask features include sessions with secure cookies, pluggable views, and signals (for notifications and subscriptions to them). Flask also uses the concept of blueprints for making application components.
These books will help you to know more about Flask:
- Flask Web Development (O'Reilly - Miguel Grinberg)
- Building Web Applications with Flask (Packt Publishing - Italo Maia)
- Learning Flask Framework (Packt Publishing - Matt Copperwaite, Charles Leifer)
- Flask Framework Cookbook (Packt Publishing - Shalabh Aggarwal)
- Instant Flask Web Development (Packt Publishing - Ron DuPlain)
- Flask Blueprints (Packt Publishing - Joël Perras)
- Flask By Example (Packt Publishing - Gareth Dwyer)