Flask App Tutorial

Hello Coders,

This article might help beginners to code a simple App using Flask, the popular Python Framework. If something relevant for a beginner is not here or you are a beginner and a section is not presented well enough, don't hesitate to ask anything in the comments section. Being almost daily on Dev, there are big chances to respond.

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Topics

Flask Introduction
Set up (aka environment)
Edit the code
Start the application
Summary

Flask Introduction

👉 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.

Flask - the official website
Flask Docs - learn what Flask has to offer in detail

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Set up

👉 To code a Flask application we need some tools properly set up in our workstation. Here is the recommended list:

Python v3 - the language used by Flask
A (free) editor: VsCode, Sublime, Atom, Notepad++

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
Python 3.8.4

If the above command returns an error please double-check the Python installation and get back here after to follow up the next steps.

Install Flask

Flask is basically a Python package and we can install it with ease via a tool shipped by Python: PIP.

$ $ pip install Flask

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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__)

@app.route('/')
def hello():
    return f'My first Flask APP!'

This simple code snippet ( also saved here ) does the following:

Import Flask, the library that we've installed in the previous step
app object is constructed by Flask. At this point, we can use all features provided by Flask
define a default route that will return a simple Hello message when someone accesses our application using the browser

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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: