Flask is a micro

web framework A web framework (WF) or web application framework (WAF) is a software framework that is designed to support the development of web applications including web services, web resources, and web APIs. Web frameworks provide a standard way to build a ...

written in

Python Python may refer to: Snakes * Pythonidae, a family of nonvenomous snakes found in Africa, Asia, and Australia ** ''Python'' (genus), a genus of Pythonidae found in Africa and Asia * Python (mythology), a mythical serpent Computing * Python (prog ...

. It is classified as a

microframework A microframework is a term used to refer to minimalistic web application frameworks. It is contrasted with full-stack frameworks. It lacks most of the functionality which is common to expect in a full-fledged web application framework, such as: * ...

because it does not require particular tools or libraries. It has no

database In computing, a database is an organized collection of data or a type of data store based on the use of a database management system (DBMS), the software that interacts with end users, applications, and the database itself to capture and a ...

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. Applications that use the Flask framework include

Pinterest Pinterest is an American social media service for publishing and discovery of information in the form of digital Bulletin board, pinboards. This includes recipes, home, style, motivation, and inspiration on the Internet using image sharing. Pint ...

and

LinkedIn LinkedIn () is an American business and employment-oriented Social networking service, social network. It was launched on May 5, 2003 by Reid Hoffman and Eric Ly. Since December 2016, LinkedIn has been a wholly owned subsidiary of Microsoft. ...

History

Flask was created by

Armin Ronacher Armin Ronacher (born 10 May 1989) is an Austrian open source software programmer and the creator of the Flask web framework for Python. He is a frequent speaker at developer conferences and has a popular blog about software development and op ...

of Pocoo, an international group of Python enthusiasts formed in 2004. According to Ronacher, the idea was originally an April Fool's joke that was popular enough to make into a serious application. The name is a play on the earlier Bottle framework. When Ronacher and Georg Brandl created a bulletin board system written in Python in 2004, the Pocoo projects Werkzeug and Jinja were developed. In April 2016, the Pocoo team was disbanded and development of Flask and related libraries passed to the newly formed Pallets project. Since 2018, Flask-related data and objects can be rendered with Bootstrap. Flask has become popular among Python enthusiasts. it has the second-most number of stars on

GitHub GitHub () is a Proprietary software, proprietary developer platform that allows developers to create, store, manage, and share their code. It uses Git to provide distributed version control and GitHub itself provides access control, bug trackin ...

among Python web-development frameworks, only slightly behind Django, and was voted the most popular web framework in the Python Developers Survey for years between and including 2018 and 2022.

Components

The microframework Flask is part of the ''Pallets Projects'' (formerly ''Pocoo''), and based on several others of them, all under a

BSD license BSD licenses are a family of permissive free software licenses, imposing minimal restrictions on the use and distribution of covered software. This is in contrast to copyleft licenses, which have share-alike requirements. The original BSD lic ...

Werkzeug

Werkzeug (

German German(s) may refer to: * Germany, the country of the Germans and German things **Germania (Roman era) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizenship in Germany, see also Ge ...

for "tool") is a utility library for the Python programming language for

Web Server Gateway Interface The Web Server Gateway Interface (WSGI, pronounced ''whiskey'' or ) is a simple calling convention for web servers to forward requests to web applications or frameworks written in the Python programming language. The current version of WSGI, ...

(WSGI) applications. Werkzeug can instantiate objects for request, response, and utility functions. It can be used as the basis for a custom

software framework In computer programming, a software framework is a software abstraction that provides generic functionality which developers can extend with custom code to create applications. It establishes a standard foundation for building and deploying soft ...

and supports Python 2.7 and 3.5 and later.

Jinja

Jinja, also by Ronacher, is a template engine for the Python programming language. Similar to the Django web framework, it handles templates in a

sandbox A sandbox is a sandpit, a wide, shallow playground construction to hold sand, often made of wood or plastic. Sandbox or sand box may also refer to: Arts, entertainment, and media * Sandbox (band), a Canadian rock music group * Sandbox (Gu ...

MarkupSafe

MarkupSafe is a

string String or strings may refer to: *String (structure), a long flexible structure made from threads twisted together, which is used to tie, bind, or hang other objects Arts, entertainment, and media Films * ''Strings'' (1991 film), a Canadian anim ...

handling library for the Python programming language. The eponymous MarkupSafe

type Type may refer to: Science and technology Computing * Typing, producing text via a keyboard, typewriter, etc. * Data type, collection of values used for computations. * File type * TYPE (DOS command), a command to display contents of a file. * ...

extends the Python string type and marks its contents as "safe"; combining MarkupSafe with regular strings automatically escapes the unmarked strings, while avoiding double escaping of already marked strings.

ItsDangerous

ItsDangerous is a safe

data serialization In computing, serialization (or serialisation, also referred to as pickling in Python (programming language), Python) is the process of translating a data structure or object (computer science), object state into a format that can be stored (e. ...

library for the Python programming language. It is used to store the session of a Flask application in a

cookie A cookie is a sweet biscuit with high sugar and fat content. Cookie dough is softer than that used for other types of biscuit, and they are cooked longer at lower temperatures. The dough typically contains flour, sugar, egg, and some type of ...

without allowing users to tamper with the session contents.

Features

* Development server and

debugger A debugger is a computer program used to test and debug other programs (the "target" programs). Common features of debuggers include the ability to run or halt the target program using breakpoints, step through code line by line, and display ...

* Integrated support for

unit testing Unit testing, component or module testing, is a form of software testing by which isolated source code is tested to validate expected behavior. Unit testing describes tests that are run at the unit-level to contrast testing at the Integration ...

RESTful REST (Representational State Transfer) is a software architectural style that was created to describe the design and guide the development of the architecture for the World Wide Web. REST defines a set of constraints for how the architecture of ...

request dispatching * Uses Jinja templating * Support for secure cookies (client side sessions) * 100%

WSGI The Web Server Gateway Interface (WSGI, pronounced ''whiskey'' or ) is a simple calling convention for web servers to forward requests to web applications or frameworks written in the Python programming language. The current version of WSGI, ve ...

1.0 compliant *

Unicode Unicode or ''The Unicode Standard'' or TUS is a character encoding standard maintained by the Unicode Consortium designed to support the use of text in all of the world's writing systems that can be digitized. Version 16.0 defines 154,998 Char ...

-based * Complete documentation *

Google App Engine Google App Engine (also referred to as GAE or App Engine) is a cloud computing platform used as a service for developing and hosting web applications. Applications are sandboxed and run across multiple Google-managed servers. GAE supports aut ...

compatibility * Extensions available to extend functionality

Example

The following code shows a simple web application that displays "

Hello World Hello World may refer to: * "Hello, World!" program, a computer program that outputs or displays the message "Hello, World!" Music * "Hello World!" (composition), song by the Iamus computer * "Hello World" (Tremeloes song), 1969 * "Hello World" ...

!" when visited: from flask import Flask app = Flask(__name__) @app.route("/") def hello() -> str: return "Hello World" if __name__

"__main__": app.run()

References

External links

* {{DEFAULTSORT:Flask (Programming) Free software programmed in Python Python (programming language) web frameworks Software using the BSD license Articles with example Python (programming language) code