flask

flask

Lightweight Python microframework with minimal core and rich extension ecosystem.

Core Concepts

• Blueprints: modular route organization with Blueprint objects, mounted at URL prefixes
• Jinja2 templates: server-side rendering with template inheritance, filters, and macros
• SQLAlchemy ORM: db.Model for declarative models, db.session for transactional queries
• App factory: create_app() function for configurable, testable application instances

Common Patterns

• Flask-RESTful: Resource subclasses with method-based routing for REST endpoints
• Error handlers: @app.errorhandler(404) for custom JSON or HTML error responses
• Extensions: Flask-Login for auth, Flask-Migrate for schema changes, Flask-Mail for email
• Request hooks: before_request/after_request for cross-cutting concerns like DB sessions

Best Practices

• Use the app factory pattern to enable multiple config profiles (dev, test, production)
• Keep configuration in environment variables with app.config.from_prefixed_env()
• Organize views into blueprints by domain rather than dumping all routes in one file
• Use g object sparingly for request-scoped data, clean up with teardown_appcontext

Common Code Patterns

• Blueprint("auth", __name__, url_prefix="/auth") with register_blueprint in factory
• db.relationship("Post", backref="author", lazy="dynamic") for one-to-many ORM access