Flask is a free and open-source micro web framework for Python designed to help developers build secure, scalable, and maintainable web applications.

Flask is based on Werkzeug and uses Jinja2 as a template engine.

Also, it is known as a micro-framework because it doesn't require any particular third-party libraries and tools. 

However, Flask can support extensions that are implemented in Flask itself to add features into a Flask application.

Here at LinuxAPT, as part of our Server Management Services, we regularly help our Customers to perform Software Installation task on Ubuntu Systems.

In this context, we shall look into method to install the Flask framework on your Ubuntu 20.04 machine.

How to install Flask on Ubuntu ?

In order to install Flask on Ubuntu 20.04, let’s update the system first with the following command:

$ sudo apt update

Once the update is complete, go ahead to the next steps.

By default, Ubuntu 20.04 comes with Python 3.8. You can verify this by the following command:

$ python3 -V

Next, you have to install python3-venv package to create a virtual environment for the Flask application:

$ sudo apt install python3-venv

After the package is installed, let's create a virtual environment for the Flask application.

It is recommended to create a new directory for the application and navigate into it:

$ mkdir flask-dir && cd flask-dir

Now, let’s run the following command in flask-dir to create the virtual environment:

$ python3 -m venv venv

The command creates a directory named venv in flask-dir directory.

In order use the virtual environment, you have to activate it as follows:

$ source venv/bin/activate

Once the virtual environment is activated, you can install Flask using the Python package manager pip:

(venv) $ pip install Flask

Verify that the Flask is successfully installed by running the following command:

(venv) $ python -m flask --version

Congratulations, now you can create some Flask applications on your Ubuntu 20.04.

How to create a simple application with Flask on Ubuntu ?

Here, we will create a simple “Hello world” application with Flask.

Using your favorite editor to create a Python file named as: hello.py in flash-dir:

from flask import Flask
app = Flask(__name__)
def hello_world():
return 'Hello world'

In your virtual environment, run the following commands:

(venv) $ export FLASK_APP=hello.py
(venv) $ flask run

You can use your web browser or curl command to hit, you will get the "Hello world" text output.

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