What are Flask Blueprints, exactly?

Question

I have read the official Flask documentation on Blueprints and even one or two blog posts on using them.

I've even used them in my web app, but I don't completely understand what they are or how they fit into my app as a whole. How is it similar to an instance of my app but not quite? The documentation is comprehensive but I seek a layman explanation or an enlightening analogy to spark it for me. I was sufficiently perplexed when a colleague asked me to explain a Flask blueprint to them that I elected to ask here.

Answer 1

As pointed out in a comment by @Devasish, this article provides a good answer:

http://exploreflask.com/en/latest/blueprints.html

Quoting from the article:

An example of this would be Facebook. If Facebook used Flask, it might have blueprints for the static pages (i.e. signed-out home, register, about, etc.), the dashboard (i.e. the news feed), profiles (/robert/about and /robert/photos), settings (/settings/security and /settings/privacy) and many more. These components all share a general layout and styles, but each has its own layout as well

This is a very good interpretation, especially the part "if Facebook used Flask". It gives us a concrete situation to visualize how Blueprint actually works.

Answer 2

I too just stumbled up this myself and was confused after reading a few of the documentation sources. At first I thought it was like C#/Java OOP Interface Implementation style where you define some stuff but dont have to worry about it implementation details til later. However, I stumbled up this page which puts it in very very laymens (and quite hilarious present-day events) terms. https://hackersandslackers.com/flask-blueprints/

Essentially one benefit that is mentioned in the link and provides me a clear idea of it's real world usage is that I can effectively logically organize/divide the app into several parts that only need to be concerned with it's own affairs. So it provides some designed encapsulation.

Edit: I'm currently using it to segment out my webapps code. It was good decision too because I found the lead designer wants to make the frontend in Vue.js. Which I havent used yet but looking at it's project files would look far more messy and probably provide many naming collision prone instances due to files with similar names

Answer 3

For bigger projects, all your code shouldn't be in the same file. Instead you can segment or split bigger codes into separate files, mostly based on functionality. Like bricks forming a wall.

A simple Flask app

app = Flask(__name__)

A blueprinted Flask app

import from_any_module.part_1
import from_other_module.part_2

app = Flask(__name__)

app.register_blueprint(part_1)
app.register_blueprint(part_2)

A blueprint in the above app

from flask import Blueprint
part_1 = Blueprint(part_1)

@part_1.route('/url')
def function()
    return view

Answer 4

A Flask blueprint helps you to create reusable instances of your application. It does so by organizing your project in modules. Those modules are then registered the main application. They help in creating an application factory.