python 50 lines · 7 steps

Class-based config in a Flask app factory

One base config plus per-environment subclasses feed a Flask app factory that wires up extensions and blueprints.

Explained by highlit

Flask Intermediate configuration app-factory inheritance environment-variables dependency-injection

1import os
2from datetime import timedelta
3 
4 
5class BaseConfig:
6    SECRET_KEY = os.environ.get("SECRET_KEY", "dev-only-insecure-key")
7    SQLALCHEMY_TRACK_MODIFICATIONS = False
8    JSON_SORT_KEYS = False
9    PERMANENT_SESSION_LIFETIME = timedelta(days=7)
10    RATELIMIT_STORAGE_URI = os.environ.get("REDIS_URL", "memory://")
11 
12 
13class DevelopmentConfig(BaseConfig):
14    DEBUG = True
15    SQLALCHEMY_DATABASE_URI = os.environ.get(
16        "DATABASE_URL", "sqlite:///dev.db"
17    )
18    SQLALCHEMY_ECHO = True
19 
20 
21class TestingConfig(BaseConfig):
22    TESTING = True
23    SQLALCHEMY_DATABASE_URI = "sqlite:///:memory:"
24    WTF_CSRF_ENABLED = False
25 
26 
27class ProductionConfig(BaseConfig):
28    DEBUG = False
29    SQLALCHEMY_DATABASE_URI = os.environ["DATABASE_URL"]
30    SESSION_COOKIE_SECURE = True
31    PREFERRED_URL_SCHEME = "https"
32 
33 
34config = {
35    "development": DevelopmentConfig,
36    "testing": TestingConfig,
37    "production": ProductionConfig,
38}
39 
40 
41def create_app(config_name=None):
42    app = Flask(__name__)
43    config_name = config_name or os.environ.get("FLASK_ENV", "development")
44    app.config.from_object(config[config_name])
45    app.config.from_prefixed_env()
46 
47    db.init_app(app)
48    migrate.init_app(app, db)
49    app.register_blueprint(api_bp, url_prefix="/api")
50    return app

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STEP 01

Walkthrough

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Three takeaways

1Inheriting from a base config keeps shared defaults in one place while each environment overrides only what differs.
2An app factory lets you build fresh, independently-configured app instances — essential for testing and multiple deployments.
3Reading secrets and URIs from the environment keeps configuration out of source control and portable across machines.

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