flask

name flask description Best practices for Flask web development including routing, blueprints, and testing. Skill: Flask Best practices for Flask web development including routing, blueprints, and testing. When to Use Apply this skill when building Flask web applications or APIs — routing, blueprints, extensions, and testing. Project Structure Use the application factory pattern ( create_app() ) to avoid global state and enable testing. Organize features into Blueprints; register them in the factory. Keep configuration in a config.py with classes like DevelopmentConfig , ProductionConfig . Routing and Views Prefer explicit HTTP method decorators ( @app.get , @app.post ) over generic @app.route with methods=[...] . Validate request data early; return 400 errors for malformed input before processing. Use flask.abort() with appropriate HTTP codes rather than returning error responses manually. Extensions Initialize extensions lazily with ext.init_app(app) inside the factory, not at module level. Common extensions: Flask-SQLAlchemy, Flask-Migrate, Flask-Login, Flask-WTF, Flask-CORS. Testing Use app.test_client() for HTTP-level tests and app.test_request_context() for unit tests. Use pytest fixtures to create the app and client; scope appropriately ( session for the app, function for the client). Set TESTING=True and use a separate test database. Pitfalls Never use the development server ( app.run() ) in production — use Gunicorn or uWSGI. Avoid storing mutable state on the app object; use g for request-scoped data. Never hardcode SECRET_KEY — load from environment variables.