March 31


Flask in Python Simplified – Part 1

By Gulab Chand

March 31, 2020

Flask in Python – In this Series, we are going to learn the complete Flask framework step by step. This is part one of this series.

Flask is a lightweight Python framework mainly used to develop web apps. Flask is one of the most popular python web apps frameworks. It is based on the Pocoo projects Werkzeug and Jinja2. I usually use flask for deploying machine and deep learning models for end-users.

The learning curve for flask is easy to compare to other python web application framework.

In this tutorial, we are going to learn how to install flask in python on windows.

Python must be installed in your system before following steps below

So Lets Start Without wasting further time…


Here I am going to use a practical approach directly. Lets Start with Hello Flask App in Flask

  • First Create a folder in your system where you want to develop the flask app.

  • In my case, I have created a folder in the flask folder name App and inside that, I created folder name Hello.

  • Open the Command prompt and go to that folder location using the CD command 

  • And create a virtual environment first for that on command prompt write command like this

  • G:/Flask/Apps/Hello> py -m venv env env is the name of the environment 
  • Than activate environment by writing following command in command prompt  G:/Flask/Apps/Hello>env\Scripts\activate
  • Once it is done install flask with the following command – G:/Flask/Apps/Hello>pip install flask

Please see the screenshot below for all above commands

Flask Installation

Once the installation is done


  • Create a file in your app folder(My case its  Hello) using your favorite editor. I am using Notpad++.(You can use whatever editor you want to use or comfortable with)
  • Set file to run for the environment via command (env) G:\Flask\Apps\Hello>Set 
  • As our file name is  So when we run environment it will automatically run this file 
  • Now let’s write code in our file.
  • Hello Flask Program


  •  Line 1 We are importing flask library from Flask class
  • Line 3 we instantiate the class.
  • Line 5 we are creating a route. means URL which we are going to use.
  • Line 7 we are defining the method  name index.
  • In that method, we just simply return the Html code “Hello Flask!” with header tag.
  • Once we have done with this save the file and back to command prompt
  • Run the below command on prompt(env) G:\Flask\Apps\Hello>flask run
  • If everything goes well your First Flask code is ready to run
  • Open URL in your browser and you have done.Hurry, Your First flask app is ready !!!


Hello Flask in Python program


Once you did that and want to go out from env 


Type command 


(env) G:\Flask\Apps\Hello> deactivate


I hope this helps you to install Flask in python and creating your first program in the flask.


There is one more way to run Flask App. Let’s see that too

Another approach to run flask App

In this approach add the following code in existing code of  at the end of that file

if __name__ == ‘__main__’:


and now directly run the below command without activating environment as we have done previously


It will run app the same way, by default it will use port number 80. And if this port is busy with some other service in your system in that case you have to specify the port as code shown below. Otherwise, it will not start the webserver.


instead of that

put this code’′, port=5000)

now it will take port 5000 and you can open  URL in your browser and you have done.


Next tutorials we are going to discuss some other interesting aspects flask in python and routing in the flask

Gulab Chand

About the author

Gulab Chand Tejwani is an independent consultant.He is a Project Management professional (PMP) and Microsoft Certified Trainer (MCT). He has more then 15 years of experience in Microsoft technologies like Aspnet,SharePoint,Sql server and Cloud Computing as well as in Big Data and Hadoop,Mobile App development.He has also worked as technical project manager..