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An example of a large scale Flask application using blueprints and extensions.

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Quickly run the project using docker and docker-compose:

docker-compose up -d

Create the database and seed it with some data:

docker-compose run --rm app flask create-db
docker-compose run --rm app flask populate-db --num_users 5

Download front-end dependencies with yarn:

yarn install --modules-folder ./app/static/node_modules


The following environment variables are optional:

Name Purpose
APP_NAME The name of the application. i.e Flask Bones
MAIL_PORT The port number of an SMTP server.
MAIL_SERVER The hostname of an SMTP server.
MEMCACHED_HOST The hostname of a memcached server.
MEMCACHED_PORT The port number of a memcached server.
POSTGRES_HOST The hostname of a postgres database server.
POSTGRES_PASS The password of a postgres database user.
POSTGRES_PORT The port number of a postgres database server.
POSTGRES_USER The name of a postgres database user.
REDIS_HOST The hostname of a redis database server.
REDIS_PORT The port number of a redis database server.
SECRET_KEY A secret key required to provide authentication.
SERVER_NAME The hostname and port number of the server.


Caching with Memcached

from app.extensions import cache

# Cache something
cache.set('some_key', 'some_value')

# Fetch it later

Email delivery

from app.extensions import mail
from flask_mail import Message

# Build an email
msg = Message('User Registration', sender='', recipients=[])
msg.body = render_template('mail/registration.mail', user=user, token=token)

# Send

Asynchronous job scheduling with RQ

RQ is a simple job queue for python backed by redis.

Define a job:

def send_email(msg):

Start a worker:

flask rq worker

Queue the job for processing:


Monitor the status of the queue:

flask rq info --interval 3

For help on all available commands:

flask rq --help

Stupid simple user management

from app.extensions import login_user, logout_user, login_required

# Login user

# You now have a global proxy for the user

# Secure endpoints with a decorator

# Log out user

Password security that can keep up with Moores Law

from app.extensions import bcrypt

# Hash password
pw_hash = bcrypt.generate_password_hash('password')

# Validate password
bcrypt.check_password_hash(pw_hash, 'password')

Easily swap between multiple application configurations

from app.config import dev_config, test_config

app = Flask(__name__)

class dev_config():
    DEBUG = True

class test_config():
    TESTING = True

# Configure for testing

# Configure for development

Form validation & CSRF protection with WTForms

Place a csrf token on a form:

{{ form.csrf_token }}

Validate it:


Rate-limit routes

from app.extensions import limiter

@limiter.limit("5 per minute")
@auth.route('/login', methods=['GET', 'POST'])
def login():
    # ...
    return 'your_login_page_contents'

Automated tests

Run the test suite:


Use any relational database using the SQLAlchemy ORM

from app.user.models import User

# Fetch user by id
user = User.get_by_id(id)

# Save current state of user

# Fetch a paginated set of users
users = User.query.paginate(page, 50)

Front-end asset management

Download front-end dependencies with yarn:

yarn install --modules-folder ./app/static/node_modules

Merge and compress them together with Flask-Assets:

flask assets build

Version your database schema

Display the current revision:

flask db current

Create a new migration:

flask db revision

Upgrade the database to a later version:

flask db upgrade

Internationalize the application for other languages (i18n)

Extract strings from source and compile a catalog (.pot):

pybabel extract -F babel.cfg -o i18n/messages.pot .

Create a new resource (.po) for German translators:

pybabel init -i i18n/messages.pot -d i18n -l de

Compile translations (.mo):

pybabel compile -d i18n

Merge changes into resource files:

pybabel update -i i18n/messages.pot -d i18n