Flask Extensions

Some useful Flask extensions

Listed below are extensions that can be added to your existing codebase:

Flask-Mail

A web-based program is frequently necessary to include functionality that allows users/clients to send emails. Creating a simple interface with any email server is a breeze with the Flask-Mail extension.

Flask-WTF

WTForms is a form rendering and validation library with a lot of flexibility. With this WTForms library, the Flask-WTF extension provides a straightforward interface. We may construct form fields in our Python script and render them using an HTML template using Flask-WTF. Validation can be applied to the WTF field as well.

Flask-SQLAlchemy

Performing CRUD tasks on a database using raw SQL in Flask web apps can be complex. Instead, SQLAlchemy, a Python toolkit, is a robust OR Mapper that allows application developers complete access to SQL's power and flexibility. Flask-SQLAlchemy is a Flask plugin that adds SQLAlchemy support to your Flask project.

Flask-Sijax

Sijax stands for 'Simple Ajax,' and it's a Python/jQuery package that integrates Ajax into your application a breeze. It uses jQuery.ajax to make AJAX requests.

How to add extensions?

Installation, configuration, and usage instructions may all be found in the documentation for each extension. In most cases, extensions get their configuration from app.config and are given an application instance during initialization. For example, an extension called "Flask-Foo" could be used in the following way:

from flask_foo import Foo

foo = Foo()

app = Flask(__name__)
app.config.update(
    FOO_BAR='baz',
    FOO_SPAM='eggs',
)

foo.init_app(app)

How to build extensions?

Let us get started with creating such a Flask extension. The extension we want to make here will provide fundamental support for SQLite3.
First, we create the following folder structure:

flask-sqlite3/
    flask_sqlite3.py
    LICENSE
    README

Here are the contents of the most important files:
setup.py: The following file is used to install your Flask extension. As you can see in the following code, you import the setuptools. You fill basic information about your extension like the extension’s name, version, url, your name(author), your email and so on. 

from setuptools import setup
setup(
    name='Flask-SQLite3',
    version='1.0',
    url='http://example.com/flask-sqlite3/',
    license='BSD',
    author='Your Name',
    author_email='your-email@example.com',
    description='Very short description',
    long_description=__doc__,
    py_modules=['flask_sqlite3'],
    zip_safe=False,
    include_package_data=True,
    platforms='any',
    install_requires=[
        'Flask'
    ],
    classifiers=[
        'Environment :: Web Environment',
        'Intended Audience :: Developers',
        'License :: OSI Approved :: BSD License',
        'Operating System :: OS Independent',
        'Programming Language :: Python',
        'Topic :: Internet :: WWW/HTTP :: Dynamic Content',
        'Topic :: Software Development :: Libraries :: Python Modules'
    ]
)

Many extensions will need some form of initialization step. You can initialize your extension either using initialization functions or classes. For this extension, we will use the class-based approach. This approach will provide users with an object that handles opening and closing database connections.

flask_sqlite3.py: This is where your extension code goes. 
So what is the code doing?

• The __init__ method takes an optional app object and will call init_app.
• The init_app method exists so that the SQLite3 object can be instantiated without requiring an app object. This method supports the factory pattern for creating applications. The init_app will set the configuration for the database, defaulting to an in-memory database if no configuration is supplied. In addition, the init_app method attaches the teardown handler.
• We define a connect method that opens a database connection.
• We add a connection property that opens the database connection on first access and stores it in the context.
• Note here that we’re attaching our database connection to the top application context via _app_ctx_stack.top. 

import sqlite3
from flask import current_app, _app_ctx_stack

class SQLite3(object):
    def __init__(self, app=None):
        self.app = app
        if app is not None:
            self.init_app(app)

    def init_app(self, app):
        app.config.setdefault('SQLITE3_DATABASE', ':memory:')
        app.teardown_appcontext(self.teardown)

    def connect(self):
        return sqlite3.connect(current_app.config['SQLITE3_DATABASE'])

    def teardown(self, exception):
        ctx = _app_ctx_stack.top
        if hasattr(ctx, 'sqlite3_db'):
            ctx.sqlite3_db.close()

    @property
    def connection(self):
        ctx = _app_ctx_stack.top
        if ctx is not None:
            if not hasattr(ctx, 'sqlite3_db'):
                ctx.sqlite3_db = self.connect()
            return ctx.sqlite3_db

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FAQs

1. Do we need a license for our flask extensions?
   Flask extensions must be released under a BSD, MIT, or more liberal license to be featured in the Flask Extension Registry. Remember that the Flask Extension Registry is a moderated environment, and libraries will be tested to see if they behave as expected before being accepted.
    
2. Which flask extension can be used to integrate Amazon Alexa into our application?
   Flask-Ask is an extension that allows you to create Amazon Alexa skills using the familiar Flask functions structure.
    
3. Which flask extension makes using bootstrap on our website easier?
   Flask-bootstrap makes it easy to use the Bootstrap CSS framework with less boilerplate code in your Flask apps.

Key Takeaways

From this article, we learn about flask extensions, using them, some helpful flask extensions, and building our extensions. 
But this is not enough; you need something extra to excel in web development truly. If you want to learn more about web development, you can read our articles or take our highly curated Web Development course.