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Flask Blueprints
Flask Blueprints

Flask Blueprints: Dive into the world of the Flask microframework to develop an array of web applications

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Flask Blueprints

Chapter 2. Small to Big – Growing the Flask Application Structure

Flask is a wonderful framework for people who want to write a very quick single-file application in order to prototype an API or to build a drop-dead simple website. What isn't immediately obvious, however, is just how flexible and adept Flask is at growing in larger, more modular application structures that are a necessity once the single-module layout becomes more burdensome than convenient. The major points that we will cover in this chapter are as follows:

  • How to convert a module-based Flask application to a package-based layout
  • How to implement Flask blueprints on top of a package-based application structure
  • How to ensure that our resulting application can be run with the built-in Werkzeug development server

Your first Flask application structure

The canonical Flask introductory application that is found on the official website is a paragon of simplicity, and is something you've most likely come across beforehand:

# app.py 
from flask import Flask
app = Flask(__name__)

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

if __name__ == "__main__":
app.run()

The preceding application can be run by first installing the Flask package from pip (all in a virtual environment, of course) and then executing the script itself under the Python interpreter:

$ pip install Flask
$ python app.py

This will start the Werkzeug development web server, which was installed when Flask was obtained via pip, and serve the application on http://localhost:5000 by default.

The typical way in which people start a new Flask application is to add various endpoints to the incredibly simple module that we showed in the preceding section:

from flask import Flask, request
app = Flask(__name__...

From module to package

The simplest structural change that can be applied to a module-based Flask application is to transform it into a typical Python package, with special accommodation for the static and templates folders.

application
└──application
    ├──__init__.py
    ├──static
    │  ├──app.js
    │  └──styles.css
    └──templates
         ├──index.html
         └──layout.html

Here, we created a top-level application package, moved the app.py module along with the static and template folders inside it, and renamed it __init__.py.

Note

The __init__.py file is required for a folder to be considered a valid Python package.

One detail that should be handled at this point is the code that is used to run the development server. If you recall, the single-module application contained the following conditional statement...

From package to blueprint

The package-based application structure that we just explored may be suitable for a large number of applications. However, Flask offers us a level of abstraction née Blueprints, which formalizes and enforces a separation of concerns at the level of views.

Note

Do not confuse the concept of a blueprint in Flask, which is an abstraction to factor an application into more discrete components, with that of the Packt book series by the same name!

A Flask application that has become too unwieldy can be factored into a set of discrete blueprints—each with their own mapping of URIs and view functions, static resources (for example, JavaScript and CSS files), Jinja templates, and even Flask extensions. In many respects, blueprints are very similar to the Flask applications themselves. However, a blueprint is not an independent Flask application and cannot be run independently as an application itself, as described in the official Flask documentation:

A blueprint...

Summary

In this chapter, we started out with the most common, simple Flask application architecture and explored a few of the ways in which we can extend it in order to allow for a more modular approach. We first went from a module-based layout to a package-based one and then graduated to the use of Flask blueprints, which paved the way for the basic application structure that we will use in the following chapters.

In the next chapter, we will use the knowledge that we gained here to create our first functional Flask application by utilizing the blueprint pattern and several well-known Flask extensions.

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Description

Flask is a small but powerful web development framework for Python. Though Flask is termed a micro-framework, it is no way lacking in functionality; there are many extensions available to Flask which helps it to function at the same level as other large frameworks such as Django and Ruby on Rails. This book will demonstrate how to develop a series of web application projects with the Python web micro-framework, and leverage extensions and external Python libraries and APIs to extend the development of a variety of larger and more complex web applications. The book will start by explaining Python’s Virtualenv library and how to create and switch between multiple virtual environments. You’ll first build an SQL database-backed application, which will use Flask-WTF, Flask-SQLAlchemy, Jinja templates, and other methods. Next you’ll move on to a timeline application, built using concepts including pytest-Flask, the Blinker package, data modelling for user timelines, exception handling, and creating and organizing CLI tools. Moving on, you’ll discover how to implement a photo timeline application where you’ll explore topics such as writing and running celery tasks, API error handling and testing, and Werkzeug middlewares. Finally, the book walks you through creating an application which fetches data from GitHub and stores it locally. You will also learn how to install and configure Flask-Click extension.

Who is this book for?

If you are a Python web developer who has developed basic Flask applications and now wants to build a series of more complex web applications, then this is the book for you.

What you will learn

  • Use the virtualenv Python package to effectively isolate your development environments
  • Convert a simple onefile Flask application into a more fullfledged multipackage application
  • Integrate FlaskLogin for simple user authentication, FlaskWTF for forms, and FlaskSQLAlchemy for database interactions
  • Explore URL routing and dispatching in a blueprint structured application
  • Create your own signals and consume them within your application
  • Learn to leverage Werkzeug, the WSGI library that powers much of Flask
  • Implement custom exceptions for handling non20x response codes
  • Write your own CLI tools for administrative and development tasks of your Flask application using FlaskScript/Click
  • Build your Flask extensions to encapsulate reusable behaviors across your applications
  • Integrate your application with open source JavaScriptbased graphing libraries to create simple data visualizations

Product Details

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Publication date : Nov 27, 2015
Length: 198 pages
Edition : 1st
Language : English
ISBN-13 : 9781784397340
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Product Details

Publication date : Nov 27, 2015
Length: 198 pages
Edition : 1st
Language : English
ISBN-13 : 9781784397340
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Table of Contents

8 Chapters
1. Starting on the Right Foot – Using Virtualenv Chevron down icon Chevron up icon
2. Small to Big – Growing the Flask Application Structure Chevron down icon Chevron up icon
3. Snap – the Code Snippet Sharing Application Chevron down icon Chevron up icon
4. Socializer – the Testable Timeline Chevron down icon Chevron up icon
5. Shutterbug, the Photo Stream API Chevron down icon Chevron up icon
6. Hublot – Flask CLI Tools Chevron down icon Chevron up icon
7. Dinnerly – Recipe Sharing Chevron down icon Chevron up icon
Index Chevron down icon Chevron up icon

Customer reviews

Rating distribution
Full star icon Full star icon Full star icon Half star icon Empty star icon 3.3
(3 Ratings)
5 star 33.3%
4 star 0%
3 star 33.3%
2 star 33.3%
1 star 0%
Joseph Erskine Jun 07, 2016
Full star icon Full star icon Full star icon Full star icon Full star icon 5
One of the best programming books I’ve come across. I’ve read through Flask blogs (i.e. Flask-Mega Tutorial) and never felt like I had a good grasp on the framework. The authors provides a concise, in-depth look into Flask. Highly recommend if you want to get beyond the surface level.
Amazon Verified review Amazon
Kevin Aug 10, 2016
Full star icon Full star icon Full star icon Empty star icon Empty star icon 3
It needs a proper code review.It may sound harsh, but this reminded me of one of those projects you get hired on to fix something that never worked. When they show you the code, it's like the former guy just stopped working and left. I spent a few hours fixing problems and at page 50 threw in the towel. The point is to learn the framework, not debug the code.
Amazon Verified review Amazon
Roger Pence Feb 13, 2016
Full star icon Full star icon Empty star icon Empty star icon Empty star icon 2
This book continues Packt's grand tradition of poor tech reviews of the code presented. The code in the book, and the book's accompanying downloadable is wrong in several places. Note to self: only buy books where the code is on GitHub!All that said, the author taught me a couple of things and I'll give him another try--if he finds a better publisher.
Amazon Verified review Amazon
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