flask.md

The flask Package

The flask package provides a micro-framework for making web applications and APIs.

References

• Website
• Docs
• Source
• Quick-start Guide
• Tutorial
• Jinja Templates

Installation

First install flask, if necessary:

pip install flask

Usage

Follow the "Web Application" Exercise for an introduction to making web applications with Flask.

For your reference, here are some Flask app templates which implement more advanced set of functionality. Feel free to copy the templates and build on top of them as desired:

Web App Template Repo	Login	Datastore	Comments
flask-firebase-template-2022	Google Login	Firestore
flask-sheets-starter-2023	Google Login	Google Sheets	Simple example.
flask-sheets-template-2023	Google Login	Google Sheets	Full example with tests and CI.
flask-spotify-template-2023	Spotify Login	N/A

App Initialization

Example application factory function:

# this is the "web_app/__init__.py" file...

from flask import Flask

from web_app.routes.home_routes import home_routes
#from web_app.routes.other_routes import other_routes

def create_app():
    app = Flask(__name__)
    app.register_blueprint(home_routes)
    #app.register_blueprint(other_routes)
    return app

if __name__ == "__main__":
    my_app = create_app()
    my_app.run(debug=True)

Routes

Example routes:

# this is the "web_app/routes/home_routes.py" file...

from flask import Blueprint, request, render_template

home_routes = Blueprint("home_routes", __name__)

@home_routes.route("/")
@home_routes.route("/home")
def index():
    print("HOME...")
    return "Welcome Home"
    #return render_template("home.html")

@home_routes.route("/about")
def about():
    print("ABOUT...")
    return "About Me"
    #return render_template("about.html")

@home_routes.route("/hello")
def hello_world():
    print("HELLO...")

    # if the request contains url params, for example a request to "/hello?name=Harper"
    # the request object's args property will hold the values in a dictionary-like structure
    url_params = dict(request.args)
    print("URL PARAMS:", url_params) #> can be empty like {} or full of params like {"name":"Harper"}

    # get a specific key called "name" if available, otherwise use some specified default value
    # see also: https://www.w3schools.com/python/ref_dictionary_get.asp
    name = url_params.get("name") or "World"

    message = f"Hello, {name}!"
    return message
    #return render_template("hello.html", message=message)

Testing Flask Applications

See: https://flask.palletsprojects.com/en/2.1.x/testing/

After you have implemented a web application, if you would like to test it, consider the following examples...

Testing a web application:

import pytest

from web_app import create_app

@pytest.fixture(scope="module")
def test_client():
    app = create_app()
    app.config.update({"TESTING": True})
    return app.test_client()

def test_home(test_client):
    response = test_client.get("/")
    assert response.status_code == 200
    assert b"<h1>Home</h1>" in response.data

def test_about(test_client):
    response = test_client.get("/about")
    assert response.status_code == 200
    assert b"<h1>About</h1>" in response.data

def test_products(test_client):
    response = test_client.get("/products")
    assert response.status_code == 200
    assert b"<h1>Products</h1>" in response.data
    
    assert b"Textbook" in response.data
    assert b"Cup of Tea" in response.data
    assert b"Strawberries" in response.data

Testing Flask APIs:

import pytest

from api import create_app

@pytest.fixture
def api_client():
    app = create_app()
    return app.test_client()

def test_my_endpoint(api_client):
    response = api_client.get("/api/v1/my_endpoint")
    parsed_response = json.loads(response.data)
    assert response.status_code == 200
    assert isinstance(parsed_response, list)
    # etc.