Intro to Flask Part 1

Baby's First Flask App

Create app folder

mkdir hello-flask

Create a virtual environment

python -m venv venv

Activate the virtual environment

source venv/bin/activate

Install Flask

pip install flask

Create an app.py file and add this:

from flask import Flask


app = Flask(__name__)

Start the server

flask run

This starts a server on port 5000 and… does nothing.

GET Routes

To respond to GET requests from a client:

@app.route('/')
def index():
    print('Index route / hit')

Web servers are long-running processes. If you make any changes to the code, you'll need to stop the server with Control-c and then start it again with flask run.

Once you're restarted the server, visit localhost:5000 in your web browser, you should see the text "Index route / hit" in your terminal but nothing in your web browser.

To send a response back to the browser, you can return something:

@app.route('/')
def index():
    print('Index route / hit')
    return 'Home Page'

Restart the server and reload localhost:5000. You should now see the text Home Page in the web browser.

Automatically Restarting the Server

Restarting the server manually any time you want to test changes to the code is tedious. Using the --debug flag, you can automate this process and streamline your workflow.

flask --debug run

Add Another Route

@app.route('/hello)
def hello():
    return 'Hello World'

Visit localhost:5000/hello in your web browser.