General-purpose, high-level programming language supporting multiple programming paradigms.


Flask is a micro web framework for Python, based on the Werkzeug toolkit and Jinja2 template engine.

Installation of Flask in the virtualenv

It’s recommended to keep your project inside virtual environment. Let’s install and create a new virtual environment for your project.

At first open the Terminal (press Alt + F1, type Terminal and click on the black squere icon or just press Enter). Second, create a new folder my_project open it.

$ mkdir my_project
$ cd my_project

Let’s create a virtual environment called project_venv which will contain Python and pip which you can use to install Flask.

$ python3 -m venv project_venv

If you want to work in the virtual environment, you have to activate it.

$ source project_venv/bin/activate

Running the virtual environment, you can install Flask.

(project_venv) $ pip install flask

That is all, you have sucessfully installed Flask in the virtual environment! Now you can start working on your project.

First application

This is an example of how a minimal Flask application can look like.

from flask import Flask
app = Flask(__name__)

def hello_world():
    return "Hello World!"

if __name__ == "__main__":


Assuming that you have some Flask application called, you can run it in your activated virtual environment (see above) like this.

(project_venv) $ python3
 * Running on

You should see that it is running on some address, in this case Default port for Flask applications is 5000. Open it in web browser to see your application.

When you finish your work, just deactivate the virtual environment.

(project_venv) $ deactivate

What next?

Authors: Adam Samalik, Avi Wollman, Dominika Krejčí, Jakub Kadlčík, Josef Stribny