Flask Blueprints for modular MVC like web applications

flask_blueprints

Skill - Flask Blueprints for modular MVC like web applications

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In this post we will learn how to use flask blueprints for creating modular MVC like web applications

What is a Flask Blueprint

A group multiple Flask routes can be segregated as a Flask Blueprint
Each blueprint can be used like an MVC controller by registering each blueprint at a URL prefix
Routes can be moved from the main server file into blueprints to reduce the lines of code
flask url_for function can be used to easily used to create relative URLs for a route within a blueprint or for a specific blueprint route

Create a Flask Blueprint

# src/controllers/books.py
from flask import Blueprint, render_template

booksCtrlr = Blueprint('books', __name__)

@booksCtrlr.route('/')
def list():
    return render_template("books/list.html")

@booksCtrlr.route('/<int:id>')
def getItem(id: int):
    return render_template("books/detail.html", id=id)

A blueprint can be created from the Blueprint class imported from flask
Functions can be declared as routes using annotations. For example, a route can be added to a blueprint named booksCtrlr using an annotation like @booksCtrlr.route('/')

Add a blueprint to the flask application under a URL prefix

# server.py
from flask import Flask, render_template
from src.controllers.books import booksCtrlr
from src.controllers.authors import authorsCtrlr

app = Flask(__name__)

@app.route('/')
def index():
    return render_template("home.html")

app.register_blueprint(booksCtrlr, url_prefix="/books")
app.register_blueprint(authorsCtrlr, url_prefix="/authors")

app.run(host="0.0.0.0", port=50100, debug=True)

In the above example, the blueprint object is imported in the server file using from src.controllers.books import booksCtrlr
Then the blueprint is mounted to the main application named app at a prefix /books using app.register_blueprint(booksCtrlr, url_prefix="/books")

generate URLs to flask blueprint routes using “url_for”

<!-- templates/books/list.html file -->
<html>

<h2>List of Books</h2>
<ul>
    <li><a href="{{url_for('.getItem', id=1)}}">Item1</a></li>
</ul>

<a href="{{url_for('index')}}">Back to Home</a>
<br>
<a href="{{url_for('authors.list')}}">Authors</a>
</html>

In the above example, the URL to the flask route function getItem within the same blueprint can be generated using url_for('.getItem', id=1). Hence relative URLs with in the same blueprint can be generated using the ‘.’ (dot) notation.
The URL for flask route function list within the blueprint authors can be generated using url_for('authors.list')
Hence URLs for routes inside blueprints can be generated using the ‘.’ (dot) notation
The URL for the route function ‘index’ in the main server can be generated using url_for('index')

Video

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References

Official flask blueprints docs - https://flask.palletsprojects.com/en/latest/blueprints/

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