Explain the role of Flask in Python Programming?

Web apps were developed to generate the content based on retrieved data that changes based on the user interaction with the website. The server side here is responsible for querying, retrieving as well as updating the data. This makes the web applications to be slower and more complicated to deploy in comparison with simple small websites A typical web application ecosystem consists of two primary coding environments namely client as well as server-side scripting. In the Client-side system, the code executed on the user browser is visible to anyone who has the access to the system in the generation of the first results. On the other hand, server-side scripting run on the backend of the webserver. This enables developers to design, build maintains and host web applications over the internet. Today in the article, we are going to discuss the flask() application in python programming.

Before going to know about flask(), let us start our discussion with the web application.

A web application framework is a collection of modules and libraries that allows helps developers to write applications without writing the low-level codes such as protocols, thread management, etc. Flask is an API that allows programmers to build up web applications. The Flask framework is more explicit than the Django framework and is easier to learn because it has less code to implement a simple web-based application. Flask is based on Web Server Gateway Interface (WSGI) tool kit and the Jinja2 template engine.

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To understand the flask, we initially need to understand the following terms:

WGSI: WSGI (Web Server Gateway Interface) has been adopted as a standard for Python web application development. WSGI is a specification for the universal interface between web servers as well as web applications.

Werkzeug: It is a WSGI toolkit that implements request, response object, and other utility functions. This enables building the framework of it. This Flask framework uses Werkzeug as one of its bases.

Jinja2: This is the most popular python templating engine. This web templating system combines the template with certain data sources to render the dynamic web pages.

Getting started with Flask:

What is Flask?

Flask is a framework that provides libraries to build lightweight applications in python. Many developers consider flask as a micro framework. This framework was developed by Armin Ronacher who leads an international group of Python enthusiasts(.

Python 2.6 (or) higher requires the installation of the flask. The programmers can start importing the Flask package on any Python IDE.  You can check out the installation of Flask with the following code:

#an object of the WSGI application

from flask import Flask 

app = Flask(__name__) # Flask constructor

# A decorator used to tell the application

# which URL is associated function


def hello():

 return 'HELLO'

if __name__=='__main__':


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In the above code, the ‘/’ URL bounds with the hello() function. If the webserver homepage is opened in a browser, the output function will be rendered accordingly.

Here the flask() is started by calling the run() function. Here the method should be restarted manually for any change in the code.  To solve this scenario, debug support is enabled to track any error.  

app.debug = True


app.run(debug = True)


The web frameworks provide a routing technique, to remember the URL’s easily. It is useful to access the web page directly,  without navigating from the home page. In python programming routing is done through the following route() decorator, a bind a URL to the function

# decorator to route URL

def hello_world():          


# binding to the function of route

return ‘hello world’

If the user visits http://localhost:5000/hello URL the output of the hello world() function will be rendered in the browser. Besides this, the add_url_rule function of the object is used to bind the URL with the function.

def hello_world():

return ‘hello world’

app.add_url_rule(‘/’, ‘hello’, hello_world)

Flask Variables:

The flask variables were responsible to dynamically build URLs by adding the variable parts to the rule parameter. The variable part here is marked as a keyword argument as shown in the example below:

 from flask import Flask

app = Flask(__name__)

# routing the decorator function hello_name


def hello_name(name):

return 'Hello %s!' % name

if __name__ == '__main__':

app.run(debug = True)

Save the file with the .py extension, and run from the power shell. Now navigate to http://localhost:5000/hello/kitsonlinetrainings.


Hello kitsonlinetrainings

In the above example, the parameter of the route() decorator contains the variable part attached to the URL ‘/hello’ as an argument. Hence if the user navigates to http://localhost:5000/hello/kitsonlinetrainings , ‘kitsonlinetrainings’ will be passed to the hello() function as an argument.  In addition to the default string variable part, other data types like int, float, and path were also used. The Flask URL rules were based on the Werkzeugs routing module. It ensures that the URLs formed are unique and precedents presents here were laid by apache.

from flask import Flask

app = Flask(__name__)


def show_blog(postID):

return 'Blog Number %d' % postID


def revision(revNo):

return 'Revision Number %f' % revNo

if __name__ == '__main__':


# says the URL is http://localhost:5000/blog/555

Flask Advantages:

Utilization of flask framework in python programming has the following advantages:

  • It is easy to use
  • Provision of a built-in server as well as the debugger
  • Provision for integrated unit test support
  • Provision for RESTful request dispatching
  • Contains the best documentation for various scenarios
  • Purely based on Unicode and WGSI 1.0
  • Contains the best documentation to explore various scenarios


In this article, we tried to understand the importance and the application of the flask() in python programming. You can get practical knowledge on the flask() from real-time working professionals through the Python Online Course. In the upcoming post of this blog, I'll be introducing the new framework. Meanwhile, you can also check out the Python Interview Questions written by Industry professionals to get placed in MNC.