What is Flask in Python? 


There are many concepts to learn about Python. From syntaxes to frameworks, beginners and even experienced developers need to understand many different concepts. One such helpful concept that provides enough flexibility to developers in enhancing the program is Flask. So, in this article, we ask, what is Flask?

What is Flask?

In simple words, Flask is one of the popular frameworks of Python, quite similar to the Django framework. However, before we get deep into this topic, let’s look into what web frameworks are.

While writing complex code, programmers do not have enough time to write low-level codes continually. So they use valuable features such as frameworks that deal with low-level concepts such as thread management, protocols, etc. Flask is one such framework. 

Flask is built on the Werkzeug WSGI toolkit and Jinja2 template engine, both of which are Pocoo products. A group of Python enthusiasts dubbed Pocoo under the leadership of Armin Ronacher created it.

How to use Flask

To use Flask, one needs to install it. Flask is compatible with Python 2.6 or the higher versions.

Installing Python Flask

To install it, you must first create an isolated environment for it, and this is achieved with the help of a virtual Python environment builder called virtualenv.

virtualenv helps users create multiple environments side by side and allows you to work on numerous projects simultaneously on the same machine.

To install virtualenv on windows:

pip install virtualenv

After installing, the environment is activated using the following:


To install virtualenv on Linux:

Sudo apt-get install virtualenv

After installing the environment is created in,

mkdir newproj

cd newproj

virtualenv venv

After installing, the environment is activated on Linux using the following:


After the above steps, finally, Flask is installed in Python using,

pip install Flask

To test whether Flask is installed in the editor:

from flask import Flask

app = Flask(__name__) # Flask constructor


def hello_world():

   return 'Hello World’

if __name__ == '__main__':


In the above code,

  • The current module’s name (__name__) is passed as an input to the Flask function Object().
  • The Flask class’s route() function is a decorator that instructs the application which URL should be used to call the related function.

app.route(rule, options)

  • The rule parameter represents the function’s URL binding.
  • The parameters to be passed to the underlying rule object are listed in the options.
  • Since in this code, the URL ‘/’ is bound with the function hello_world(), the output of this function will be released when the homepage of the webserver is opened in the browser.

What is Flask Used For?

It offers a plethora of features to developers looking forward to building complex web or mobile applications. With the help of Flask, you can build blogging platforms, content sites, and many more complex applications.

To start the flask application, we use the run() function:


The above code is used to start the function, but while working on a code and making changes, the server must be reloaded on its own. But, the server does not reload on its own but manually. To avoid such minor inconvenience, we use the debug property.

Using the debug property, the server reloads on its own at every code change and will also help in tracking errors.

The debug property is added as follows:

app.debug = True


app.run(debug = True)


Another primary reason to use Flask is for its routing property.

For the users to not confuse with the URLs, web frameworks provide routing techniques helping the user remember the URLs.

Navigating directly to a web page without leaving the Home page by using routing is possible.

This is achieved by the route() decorator that binds the URL to a function:


def hello_world():

return 'hello world'

The hello-world() function is connected to the URL ‘/hello’ rule. As a result, when a visitor hits http://localhost:5000/hello, the browser will display the output of the hello world() function.

Why Use Flask?

You may use it to construct complicated and straightforward web applications and applications that are integrated with machine learning algorithms. Developers can make use of their lightweight framework to:

  • Integrated support for unit testing
  • Support for secure cookies
  • Create APIs easily
  • Supports Visual Debugging
  • Can be integrated efficiently with all the major databases integrate easily with complex databases
  • Use Ninja Templating Engine

Also, it is easier to grasp compared to other frameworks. 

Wrapping Up

Flask is a well-written, user-friendly framework. Given its expanding popularity, now is a wonderful time to study and become acquainted with this framework.

Want to be a developer?

If Flask is new to you and you’re interested in changing careers to software development, then find out more about Code Institute’s Full Stack Software Development programme by talking with one of our education advisors. Schedule a call through the form below.

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