Make a project

Set up your project folder

Each web project will need to live in its own folder. In File Explorer, go ahead and make a folder called flask_demo in your Digital Tech folder now.

Open up Visual Studio Code, select File > Open Folder… (folder, not file) and choose the flask_demo folder you created.

Your window should look something like this, with the name of the project folder in the top left:

Make sure you have the Explorer panel open (the first icon in the Activity Bar). If your mouse is in the Explorer panel, you will see icons appear next to the project name to:

• create a new file
• create a new folder,
• refresh the explorer view (if for some reason things have got out of sync with the real world),
• close all the folders in the explorer view (handy sometimes when you have a million folders open and can’t find anything)

Create application file

Create a new file, call it app.py, and copy the following code into it:

from flask import Flask
app = Flask(__name__)
 
@app.route('/')
def index():
    return 'Hello, Worldwww!'
 
if __name__ == '__main__':
    app.run(debug=True)

This is the simplest Flask app you can make. Let’s run it now. There should be a play button in the top right. This will run your Python file. You should see something like this:

The terminal will open below your editor, if it wasn’t already open, and you will see a line or two of junk which is the command that ran your script in Python. Below that you’ll see some output from Flask:

 * Serving Flask app 'app'
 * Debug mode: on
WARNING: This is a development server. Do not use it in a production deployment. Use a production WSGI server instead.
 * Running on http://127.0.0.1:5000
Press CTRL+C to quit
 * Restarting with watchdog (fsevents)
 * Debugger is active!
 * Debugger PIN: 133-237-744

You’ll notice that debug mode is on, which has caused the debugger to run, and there is a PIN listed. More on that later. For now, we’ll focus on the line Running on …. The address 127.0.0.1 is also called localhost, and is a special IP address which refers only to the local machine. It appears to be a real address, but isn’t available to other computers. What this means is that your server is only available on this computer, even if the computer is on a network. This is a useful security measure when developing web-based software.

You should be able to hold the Ctrl key and click on the URL, and it will open in a browser window. If should say:

Let’s look a bit more at what that Python code is doing.