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; 20 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 lightweight web application framework written in Python and based on the 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] Examples of applications that make use of the Flask framework are Pinterest[2], LinkedIn[3], as well as the community web page for Flask itself.[4]

Flask is called a microframework because it keeps the core simple but extensible. 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 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."[5][6]


  • 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__":

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