Code a simple app In Flask

How To code a simple Flask Application

This page explains how to code a simple Flask application.


  • Basic programming knowledge in Python

  • Basic Flask knowledge

  • Comfortable using a terminal

A minimal app

Before using Flask, we need to install it. Open a terminal and type:

$ pip install Flask

Create a new file with the following content:

from flask import Flask
app = Flask(__name__)
def hello():
return f'Hello from Flask!'

Once the file is saved, let's start the app:

$ # Set up the DEBUG environment
$ # (Unix/Mac) export FLASK_ENV=development
$ # (Windows) set FLASK_ENV=development
$ # (Powershell) $env:FLASK_ENV = "development"
$ flask run
$ # Visit the app in browser:

By visiting the app in the browser we should see "Hello from Flask" message.