Flask (web framework)

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Flask logo.svg
Developer(s)Armin Ronacher
Initial releaseApril 1, 2010; 10 years ago (2010-04-01)
Stable release
1.1.2 / April 3, 2020; 6 months ago (2020-04-03)[1][2]
Written inPython
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.[4]

Applications that use the Flask framework include Pinterest and LinkedIn.[5][6]


Flask was created by Armin Ronacher of Pocoo, an international group of Python enthusiasts formed in 2004.[7] According to Ronacher, the idea was originally an April Fool's joke that was popular enough to make into a serious application.[8][9][10]

When Ronacher and Georg Brandl created[when?] a bulletin board system written in Python, the Pocoo projects Werkzeug and Jinja were developed.[11]

Flask has become popular among Python enthusiasts. As of October 2020, it has second most stars on GitHub among Python web-development frameworks, only slightly behind Django,[12] and was voted the most popular web framework in the Python Developers Survey 2018.[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 2.7 and 3.5 and later.[14][15]


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 handles templates in a sandbox.


  • Development server and debugger
  • Integrated support for unit testing
  • RESTful request dispatching
  • Uses Jinja 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 displays "Hello World!" when visited:

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". Archived from the original on 2017-11-17.
  4. ^ "Flask Extensions". Archived from the original on 2018-05-17.
  5. ^ What challenges has Pinterest encountered with Flask?
  6. ^ Rachel Sanders: Developing Flask Extensions - PyCon 2014
  7. ^ "Pocoo Team". Archived from the original on 2018-03-15.
  8. ^ Ronacher, Armin. "Opening the Flask" (PDF). Archived from the original (PDF) on 2016-12-17. Retrieved 2011-09-30.
  9. ^ Ronacher, Armin (3 April 2010). "April 1st Post Mortem". Armin Ronacher's Thoughts and Writings. Archived from the original on 2018-05-14. Retrieved 2015-07-25.
  10. ^ "Denied: the next generation python micro-web-framework (April Fools page)". Archived from the original on 2011-09-04. Retrieved 2011-09-30.
  11. ^ "History". Pocoo Team. Archived from the original on 2017-11-19. Retrieved 2015-03-25.
  12. ^ "Python libraries by GitHub stars". Github. Retrieved 2020-01-27.
  13. ^ "Python Developers Survey 2018". www.jetbrains.com. 2018-11-01.
  14. ^ Ronacher, Armin. "Werkzeug The Python WSGI Utility Library". palletsprojects.com. Retrieved 27 May 2018.
  15. ^ Ronacher, Armin. "Installation, Python Version". palletsprojects.com. Retrieved 20 April 2020.

External links[edit]