Flask (web framework)

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Flask logo.svg
Developer(s) Armin Ronacher
Initial release April 1, 2010; 4 years ago (2010-04-01)
Stable release 0.10.1 / June 14, 2013; 21 months ago (2013-06-14)[1]
Written in Python
Operating system Cross-platform
Type Web application framework
License BSD
Website flask.pocoo.org

Flask is a micro web application framework written in Python and based on the Werkzeug toolkit and Jinja2 template engine. It is BSD licensed.

As of 2015, the latest stable version of Flask is 0.10.1.[2] Examples of applications that make use of the Flask framework are Pinterest,[3] LinkedIn,[4] as well as the community web page for Flask itself.[5]

Flask is called a microframework because it does not presume or force a developer to use a particular tool or library.[6] It has no database abstraction layer, form validation, or any other components where pre-existing third-party libraries provide common functions. However, Flask supports extensions, that can add application features as if they were implemented in Flask itself. Extensions exist for object-relational mappers, form validation, upload handling, various open authentication technologies and several common framework related tools.[7]


Flask was created by Armin Ronacher of Pocoo[8] which is an international group of Python enthusiasts formed in 2004. According to Armin, "It came out of an April Fool's joke but proved popular enough to make into a serious application in its own right.".[9][10] Flask is based on the Werkzeug WSGI toolkit and Jinja2 template engine, both of them Pocoo projects that were created when Ronacher and Georg Brandl were building a bulletin board system written in Python.[11]

Despite the lack of a major release, Flask has become extremely popular among Python enthusiasts.


  • Contains development server and debugger
  • Integrated support for unit testing
  • RESTful request dispatching
  • Uses Jinja2 templating
  • Support for secure cookies (client side sessions)
  • 100% WSGI 1.0 compliant
  • Unicode-based
  • Extensive documentation
  • Google App Engine Compatibility
  • Extensions available to enhance features desired.


The following code shows a simple web application that prints "Hello World!":

from flask import Flask
app = Flask(__name__)
def hello():
    return "Hello World!"
if __name__ == "__main__":

See also[edit]


External links[edit]