Flask is a web framework for Python that is specifically designed to provide the minimum amount of functionality that is needed to create web apps. Unlike other web frameworks, especially those in other languages, Flask does not have an entire ecosystem of libraries bundled with it for things such as database querying or form handling. Flask instead prefers to be an implementation agnostic.
The main feature of this setup is that it allows the programmer to design their app and their tools in any way they want. Not providing their own version of common abstractions also means that the standard library can be used much more often than other frameworks, which guarantees their stability and readability by other Python programmers. Because the Flask community is rather large, there are also many different community-provided ways of adding common functionality. One of the main focuses of this book is to introduce these extensions and find out how they can help avoid reinventing the wheel. The best part about these extensions is that if you don't need their extra functionality, you don't need to include them and your app will stay small.
The main downside of this setup is that the vast majority of new Flask users do not know how to properly structure large applications and end up creating an unintelligible and unmaintainable mess of code. This is why the other main focus of this book is how to create a Model View Controller (MVC) architecture with Flask apps.
Originally invented to design desktop user interfaces, the MVC setup allows the data handling (models), user interaction (controllers), and user interface (views) to be separated into three different components.
Separating these three different components allows the programmer to reuse code rather than re-implement the same functionality for each web page. For example, if the data handling code wasn't split into its own separate functions, we would have to write the same database connection code and SQL queries in each of the functions that render a web page.
A large amount of research and a lot of painful first-hand experience of what can go wrong while developing web applications has made this book the most comprehensive resource on Flask available, so I sincerely hope that you will enjoy reading it.
Chapter 1, Getting Started, helps readers set up a Flask environment for development using the best practices for Python projects. Readers are given a very basic skeleton Flask app that is built throughout the book.
Chapter 2, Creating Models with SQLAlchemy, shows how to use the Python database library SQLAlchemy in conjunction with Flask to create an object-oriented API for your database.
Chapter 3, Creating Views with Templates, shows how to use Flask's templating system, Jinja, to dynamically create HTML by leveraging your SQLAlchemy models.
Chapter 4, Creating Controllers with Blueprints, covers how to use Flask's blueprints feature in order to organize your view code while also avoiding repeating yourself.
Chapter 5, Advanced Application Structure, using the knowledge gained in the last four chapters, explains how to reorganize the code files in order to create a more maintainable and testable application structure.
Chapter 6, Securing Your App, explains how to use various Flask extensions in order to add a login system with permissions-based access to each view.
Chapter 7, Using NoSQL with Flask, shows what a NoSQL database is and how to integrate one into your application when it allows more powerful features.
Chapter 8, Building RESTful APIs, shows how to provide the data stored in the application's database to third parties in a secure and easy-to-use manner.
Chapter 9, Creating Asynchronous Tasks with Celery, explains how to move expensive or time-consuming programs to the background so the application does not slow down.
Chapter 10, Useful Flask Extensions, explains how to leverage popular Flask extensions in order to make your app faster, add more features, and make debugging easier.
Chapter 11, Building Your Own Extension, teaches you how Flask extensions work and how to create your own.
Chapter 12, Testing Flask Apps, explains how to add unit tests and user interface tests to your app for quality assurance and reducing the amount of buggy code.
Chapter 13, Deploying Flask Apps, explains how to take your completed app from development to being hosted on a live server.
To get started with this book, all you will need is a text editor of your choice, a web browser, and Python installed on your machine.
Windows, Mac OS X, and Linux users should all be able to easily follow along with the content of this book.
This book is written for web developers who are already somewhat familiar with Flask and want to take their Flask understanding from introductory to master level.
In this book, you will find a number of text styles that distinguish between different kinds of information. Here are some examples of these styles and an explanation of their meaning.
Code words in text, database table names, folder names, filenames, file extensions, pathnames, dummy URLs, user input, and Twitter handles are shown as follows: "The first() and all() methods return a value and therefore end the chain."
A block of code is set as follows:
class User(db.Model):
id = db.Column(db.Integer(), primary_key=True)
username = db.Column(db.String(255))
password = db.Column(db.String(255))
posts = db.relationship(
'Post',
backref='user',
lazy='dynamic'
)When we wish to draw your attention to a particular part of a code block, the relevant lines or items are set in bold:
from flask.ext.sqlalchemy import SQLAlchemy
app = Flask(__name__)
app.config.from_object(DevConfig)
db = SQLAlchemy(app)
Any command-line input or output is written as follows:
$ python manage.py db init
New terms and important words are shown in bold. Words that you see on the screen, for example, in menus or dialog boxes, appear in the text like this: "Hit another button that says Download Bootstrap and you will start to download a Zip file."
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