Flask (web framework)

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Flask logo.svg
Developer(s)Armin Ronacher
Initial releaseApril 1, 2010; 8 years ago (2010-04-01)
Stable release
1.0.2 / May 2, 2018; 6 months ago (2018-05-02)[1][2]
Repository Edit this at Wikidata
Written inPython
Operating systemCross-platform
TypeWeb framework

Flask is a micro web framework written in Python. It is classified as a microframework because it does not require particular tools or libraries.[3] 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. Extensions are updated far more regularly than the core Flask program.[4] Flask is commonly used with MongoDB, which gives it more control over databases and history.

Applications that use the Flask framework include Pinterest,[5] LinkedIn,[6] and the community web page for Flask itself.[7]


In 2004, Pocoo was formed as an international group of Python enthusiasts.[8] Flask was created by Armin Ronacher of Pocoo:

"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][11]

When Ronacher and Georg Brandl created[when?] a bulletin board system written in Python, the Pocoo projects Werkzeug and the Jinja2 were developed, too.[12]

Despite the lack of a major release, Flask has become extremely popular among Python enthusiasts. As of mid 2016, it was the most popular Python web development framework on GitHub.[13]


The microframework Flask is based on the Pocoo projects Werkzeug and Jinja2.


Werkzeug is a utility library for the Python programming language, in other words a toolkit for Web Server Gateway Interface (WSGI) applications, and is licensed under a BSD License. Werkzeug can realize software objects for request, response, and utility functions. It can be used to build a custom software framework on top of it and supports Python 2.6, 2.7 and 3.3.[14]


Jinja, also by Ronacher, is a template engine for the Python programming language and is licensed under a BSD License. Similar to the Django web framework, it provides that templates are evaluated in a sandbox.


  • 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]


  1. ^ https://github.com/pallets/flask/releases
  2. ^ https://pypi.org/project/Flask
  3. ^ "Flask Foreword".
  4. ^ "Flask Extensions".
  5. ^ What challenges has Pinterest encountered with Flask?
  6. ^ Rachel Sanders: Developing Flask Extensions - PyCon 2014
  7. ^ Community web page for Flask
  8. ^ "Pocoo team".
  9. ^ Ronacher, Armin. "Opening the Flask" (PDF). Retrieved 2011-09-30.
  10. ^ Ronacher, Armin (3 April 2010). "April 1st Post Mortem". Armin Ronacher's Thoughts and Writings. Retrieved 2015-07-25.
  11. ^ "Denied: the next generation python micro-web-framework (April Fools page)". Archived from the original on 2011-09-04. Retrieved 2011-09-30.
  12. ^ "Pocoo History".
  13. ^ "Python libraries by GitHub stars".
  14. ^ Ronacher, Armin. "Werkzeug The Python WSGI Utility Library". palletsprojects.com. Retrieved 27 May 2018.

External links[edit]