Flask (web framework)

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

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

Flask takes the flexible Python programming language and provides a simple template for web development. Once imported into Python, Flask can be used to save time building web applications.[citation needed] An example of an application that is powered by the Flask framework is the community web page for Flask.[2]

Flask is called a microframework because it keeps the core simple but extensible. There is no database abstraction layer, form validation, or any other components where third-party libraries already exist to provide common functionality. However, Flask supports extensions, which can add such functionality into an application as if it was implemented in Flask itself. There are extensions for object-relational mappers, form validation, upload handling, various open authentication technologies, and more.


Flask was created by Armin Ronacher. "It came out of an April Fool's joke but proved popular enough to make into a serious application in its own right."[3][4]


  • 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__":

Web applications that use Flask[edit]

See also[edit]

External links[edit]