How to Install Flask on Ubuntu

Flask is a free and open source micro web framework for Python designed to help developers build secure, scalable and maintainable web applications. It based on the Werkzeug, Jinja, MarkupSafe. It was originally created in 2010 and has since powered some of the largest websites on the internet.

Unlike Django, by default Flask doesn’t include ORM, form validation or any other functionalities provided by third party libraries. Flask is built with extensions in mind, which are Python packages that add functionality to a Flask application.

There are different methods to install Flask, depending on your needs. It can be installed system-wide or in a Python virtual environment using pip.

The main purpose of Python virtual environments is to create an isolated environment for different Python projects. In the way multiple different Flask environments on a single computer and install a specific version of a module on a per project basis without worrying that it will affect your other Flask installations. But If you install Flask into the global environment then you can install only one Flask version on your System.

Dependencies

These distributions will be installed automatically when installing Flask.

• Werkzeug implements WSGI, the standard Python interface between applications and servers.
• Jinja is a template language that renders the pages your application serves.
• MarkupSafe comes with Jinja. It escapes untrusted input when rendering templates to avoid injection attacks.
• ItsDangerous securely signs data to ensure its integrity. This is used to protect Flask’s session cookie.
• Click is a framework for writing command line applications. It provides the flask command and allows adding custom management commands.

You may like also : What is Jinja

Step 1. Install Python 3 and venv

Ubuntu 18.04 ships with Python 3.6 by default. You can verify that Python 3 is installed on your system by typing:

python3 -V

Python 3.6.6

sudo apt install python3-venv

Step 2. Create Virtual Environment

Navigate to the directory where you would like to store your Python 3 virtual environments. It can be any location where your user has read and write permissions.

Create a new directory for your Flask application and navigate into it:

mkdir my_flask_appcd my_flask_app

python3 -m venv venv

Now  you need to activate it by running the activate script:

source venv/bin/activate

Step 3. Install Flask

Now that the virtual environment is activated, you can use the Python package manager pip to install Flask:

pip install Flask

from flask import Flask
app = Flask(__name__)

@app.route('/')
def hello_world():
    return 'Hello World!'

export FLASK_APP=helloflask run

 * Serving Flask app "hello"
 * Environment: production
   WARNING: Do not use the development server in a production environment.
   Use a production WSGI server instead.
 * Debug mode: off
 * Running on http://127.0.0.1:5000/ (Press CTRL+C to quit)

deactivate