Getting Started with Flask #

Install #

Probably best to set this up in a virtual environment.

Let’s assume we’re already there.

pip3 install flask

Test installation from Python. No error? All’s good.

import flask

Setup #

In a working project directory, start with a single file. Let’s call it initial.py

from flask import Flask # Flask class
app = Flask(__name__) # instantiates a Flask application at the app variable

# routes

# route decorator - handles backend complexity for routing
# "/" bit defines the route.
# Chunk beneath that represents what actually happens.
@app.route("/") 

def hello():
    return "Hello World!"

Routes are the things typed into browsers to navigate around.

Adding extra routes is as simple as adding:

@app.route("/about")

def about():
    return "Ahoy!" # this woudl cause an about page to appear with the text "Ahoy!"

Running #

With environment variables #

tl;dr: Decorators add additional functionality to existing functions.

Prior to running (without the name/main chunk below), export variable while within working directory to point at main file:

export FLASK_APP=initial.py

To execute, run flask run from the command line. This should bring up a simple Hello world! page.

To show changes without having to reload application, run in debug mode.

export FLASK_DEBUG=1

Without environment variables #

Alternatively (my preferred way), add the following to the bottom of the script the enable the application to run with python initial.py without having to set environment variables:

if __name__ == '__main__':
    app.run(debug=True) # run the app in debug mode