Flask is a lightweight web application framework. It is designed to make getting started quick and easy, with the ability to scale up to complex applications. Compared to Django, Flask provides a lightweight codebase and more freedom to the developer. Flask is written in Python and it does not require particular tools or libraries.
To code a Flask application we need some tools properly set up in our workstation. Here is the recommended list:
To finish this tutorial we will work with the console (aka terminal). In Windows, we can use
Powershell or the corespondent
xterm for Linux. The next step is to open a terminal and check the Python installation:
$ python --version
If the above command returns an error please double check the Python installation and get back here after to follow up the next steps.
Flask is a Python package and we can install it with ease via a tool shipped by Python: PIP.
$ pip install Flask
Edit the code
Create a new file named hello.py in the current directory and add this code:
from flask import Flask
app = Flask(__name__)
return f'My first Flask APP!'
This simple code snippet ( also saved here ) does the following:
Flask, the library that we’ve installed in the previous step
appobject is constructed by
Flask. At this point, we can use all features provided by Flask
- define a defaut
routethat will return a simple Hello message when someone access our application using the browser
Start the application
Flask being such a nice framework, comes with a simple server to help us check the code without being forced to install 3rd party tools. To use it and see our minimal app running in the browser, a variable must be exported in the
environment that informs
Flask the name of the file:
$ # Set the FLASK_APP environment variable
$ # Unix/Mac
$ export FLASK_APP=hello.py
$ # Windows OS
$ set FLASK_APP=hello.py
$ # Windows OS - Powershell
$ $env:FLASK_APP = ".\hello.py"
Once we have this variable we can call
$ flask run
Flask will start the application on address ‘localhost:5000’. If we visit the aplication in the browser, we should see the message:
My first Flask APP!
Credits: See the MIT license