Flask · Lesson 5 of 15

Config Objects and the App Factory

Split development and production config and construct the app in a factory.

Beginner
14 min read
3 objectives

Before this lessonLesson 4: Blueprints, Testing and Deployment

What you will learn

Write config classes
Load from the environment
Create the app in a factory

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A single app.config["SECRET_KEY"] = "dev" does not survive contact with production. Config classes plus an application factory give you a test app, a dev app and a prod app from the same code.

Config classes

import os

class Config:
    SECRET_KEY = os.environ["SECRET_KEY"]
    SQLALCHEMY_TRACK_MODIFICATIONS = False
    SQLALCHEMY_DATABASE_URI = os.environ.get("DATABASE_URL", "sqlite:///app.db")

class DevConfig(Config):
    DEBUG = True

class TestConfig(Config):
    TESTING = True
    SQLALCHEMY_DATABASE_URI = "sqlite:///:memory:"
    WTF_CSRF_ENABLED = False

class ProdConfig(Config):
    DEBUG = False

The factory

def create_app(config_object=None):
    app = Flask(__name__)
    app.config.from_object(config_object or os.environ.get("FLASK_CONFIG", "myapp.config.DevConfig"))
    db.init_app(app)
    login_manager.init_app(app)
    from .blog import bp as blog_bp
    app.register_blueprint(blog_bp)
    return app

Tests call create_app(TestConfig). Gunicorn loads wsgi:app where app = create_app(ProdConfig).

Up next · Lesson 6Authentication with Flask-LoginSessions, password hashes and protecting views with Flask-Login.