Static vs. dynamic content

The basic idea behind HTTP is that your web browser sends a request to the webserver and the webserver tries to send the thing it asked for back. That thing might be an HTML page, a picture of a cat typing furiously at a keyboard, or a style sheet (CSS).

Static vs. dynamic

Static resources are effectively files up on the webserver that are ready to be sent straight back. The example in your editor project is the style sheet app.css which is in the directory static. If a request with that name comes in (/static/app.css), the webserver can respond immediately with that file's contents.

This is very different from the HTML files in templates. They are dynamic because — even though they might have the same resource name — their contents might be different each and every time they are requested.

For example: what's on the show buggy page? The contents of that page are different before and after you've edited your buggy. The resource has the same name, but different content.

In practice this means:

• if app.css is requested, the webserver can just send it straight back. If you added any images, they were handled the same way: see the tech note on static content.

• if a route (like /new or /) to dynamic content is requested, your Python needs to make the HTML before if can send it back: it renders the appropriate template by replacing the {{ }} and {% %} bits in it with necessary stuff, before sending it back

Knowing that, you might notice that the "routes" (like /new) you've got in your Python program are only for the dynamic content. Your program is handling the static content too, but you don't see it because anything coming in with a name that starts with static/ is automagically being handled for you.

Flask is doing this for you!

If you're wondering why you don't see explicit instructions to Python to do all that then... good thinking! Because they must be there somewhere, right? Well, they are: that's what the Flask library is doing for you. You don't need to put all that in your own program, because you did

from flask import Flask, render_template, request, jsonify

Flask is really just a Python program that knows how to behave like a webserver (specifically that's WSGI), and your program is using it. That's where things like @routes and render_template() come from and — perhaps most importantly — why your program ends with app.run()

In effect, app.py is where you define the "business logic" of what your buggy editor does. Really that's the only thing that makes it behave differently from every other webserver in the world. Once you've defined that, you hand control back to Flask by telling it to run it.

• Next: cache-busting the CSS