Any good 'first program' requires a hello world, so we're going to be building a website, in which its only goal is to return the string 'Hello World!'.
This tutorial is taken from Flasks own website.
This assumes you have completed the initial setup, such as having the latest version of Python, and a capable editor.
cd /somewhere/on/my/computer/i/want/to/put/this mkdir hello-flask cd hello-flask pwd # ensure you are where you expect to be on your system!
Covered in more detail here.
cd /somewhere/on/my/computer/i/want/to/put/this/hello-flask python3 -m venv venv . venv/bin/activate pip install Flask
cd /somewhere/on/my/computer/i/want/to/put/this/hello-flask touch app.py
Open up the newly created
app.py in your editor of choice, and fill it with this code:
from flask import Flask app = Flask(__name__) @app.route("/") def hello_world(): return "<p>Hello, World!</p>"
An overview of this code from the Flask Quickstart guide:
First we imported the Flask class. An instance of this class will be our WSGI application.
Next we create an instance of this class. The first argument is the name of the application’s module or package.
__name__is a convenient shortcut for this that is appropriate for most cases. This is needed so that Flask knows where to look for resources such as templates and static files.
We then use the route() decorator to tell Flask what URL should trigger our function.
The function returns the message we want to display in the user’s browser. The default content type is HTML, so HTML in the string will be rendered by the browser.
cd /somewhere/on/my/computer/i/want/to/put/this/hello-flask flask run
Open up your browser to http://localhost:5000/, and you should see this:
A nice empty white page with the text 'Hello, World!'