Flask Cheat Sheet
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This content was generated with the assistance of AI and should be verified against the official documentation before being relied on in production. The reference material consulted while preparing these pages is listed in the section bibliography. |
A single-page, colour-coded summary of the Flask essentials, written against Flask 3.1.3, Werkzeug 3.1.9 and
Python 3.10+ (versions verified 2026-10-07) — how to install and run an app (flask --app ... run --debug and
.flaskenv), the application factory and project layout, the configuration loaders and the key settings, the two
contexts and the order of the request lifecycle, routing, converters and url_for, request data, responses and
JSON, error handlers and hooks, blueprints, Jinja essentials, sessions and flashing, Flask-WTF and CSRF,
Flask-SQLAlchemy 2.0-style queries with db.paginate, Flask-Migrate commands, Flask-Login and Flask-JWT-Extended,
the security settings (SECRET_KEY_FALLBACKS, TRUSTED_HOSTS, cookie flags and request limits), the flask-smorest
decorators, the CLI and signals, the Celery pattern, async, gevent and Quart, streaming and Server-Sent Events,
pytest fixtures, Gunicorn, Waitress, nginx and ProxyFix, and a strip of what changed since older tutorials and
books, with a table mapping each outdated idiom to the current code — handy for quick memorization or as a
downloadable PDF desk reference.
For the full explanation, every option, and additional examples, see the dedicated pages:
Start here — Python Flask.
Foundations — Introduction & Architecture, Getting Started, Application Factory & Project Layout, Configuration, and Application & Request Lifecycle.
Routing, views and requests — Routing & URL Building, Request Data, Responses & JSON, Error Handling, Class-based Views, Hooks & View Decorators, and Blueprints.
Templates, sessions, forms and files — Jinja Templates, Static Files & Assets, Sessions, Cookies & Flashing, Forms with Flask-WTF, and File Uploads.
Data — SQLite3 and Database Basics, Flask-SQLAlchemy, Database Migrations, and NoSQL, Redis, MongoDB & Search.
Authentication, authorization and security — Authentication & Flask-Login, OAuth Social Login & LDAP, Authorization & Roles, and Security Considerations.
Building APIs — Building REST APIs, OpenAPI & API Documentation, JWT & API Authentication, and Single-Page Apps & CORS.
Extensions and ecosystem — Extensions & Ecosystem, CLI & Shell, Signals, Admin Interfaces with Flask-Admin, Internationalization with Flask-Babel, Caching, and Background Jobs, Celery & Email.
Async, streaming and real-time — Async, gevent & Quart and Streaming & Server-Sent Events.
Testing and debugging — Testing, API Contract & Property-based Testing, and Debugging, Logging & Profiling.
Production — Deployment: WSGI Servers & Proxies, Docker & Kubernetes, and Cloud Platforms & Monitoring.
Beyond the basics — Integrating LLM APIs and What’s Changed & Migration.
References
The PDF summarizes the official documentation; each source is cited in full on the page listed above that covers it, and in the section bibliography.