Flask is a micro web framework for creating APIs in Python. It’s very simple, but very powerful which is designed to get an application started quick and easy. Flask is very powerful, becuase it has the ability to scale up to complex applications.
Just because it is a micro web framework does not mean that the entire application has to fit into a single file, nor Flask is lacking in any aspects of functionality. Micro simply means Flask aims to keep the core simple but extensible, says the Flask documentation.