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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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  • 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:

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
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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 in the current directory and add this code:

from flask import Flask

app = Flask(__name__)

def hello():
    return f'My first Flask APP!'
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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:

$ export
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Once we have this variable we can call Flask:

$ flask run
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By default Flask will start the application on address 'localhost:5000'. If we visit the application in the browser, we should see the message:

My first Flask APP!

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👉 During this tutorial, we've learned a few basic things:

  • What is Flask and how to install it
  • We've coded a super simple app
  • We've seen the application running in the browser

Where to go from here?

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Btw, my (nick) name is Sm0ke and I'm pretty active also on Twitter.

Top comments (3)

andrewbaisden profile image
Andrew Baisden

Nice easy to follow guide.

sm0ke profile image
Sm0ke • Edited

Thanks for reading!
Feel free to suggest topics or access the centralized content on Github:

Flask Tutorial - Topics provided by experienced developers based on the suggestions/questions from the audience.

zoltanszogyenyi profile image
Zoltán Szőgyényi

Cool ☺️