Quart

Warnings

• breaking Quart 0.20.0 dropped support for Python 3.8. Users on Python 3.8 or earlier must upgrade their Python version to 3.9+ before upgrading to Quart 0.20.0.
  Fix: Upgrade Python to version 3.9 or higher.
• gotcha Migrating from Flask requires explicitly making view functions `async def` and using `await` for asynchronous operations. While Quart maintains Flask's API, its ASGI foundation mandates `async`/`await` for non-blocking I/O within view functions. Many Flask extensions may not work directly without `quart_flask_patch` or an async-compatible alternative.
  Fix: Rewrite view functions to be `async def` and ensure all I/O bound operations within them use `await`. For extensions, check for `quart_` prefixed versions or use `quart_flask_patch` for compatibility where possible.
• gotcha The `app.run()` method is for development purposes only and should not be used in production. For production deployments, an ASGI server like Hypercorn (which is a dependency) or Uvicorn must be used to serve the Quart application.
  Fix: Run your application with an ASGI server, e.g., `hypercorn app:app` or `uvicorn app:app` (if Uvicorn is installed).
• gotcha Calling synchronous/blocking I/O operations (e.g., traditional database drivers, `requests` library) directly within an `async def` view function without `await` or offloading them to a thread pool will block the event loop, severely degrading performance. Quart's async nature benefits from truly asynchronous libraries.
  Fix: Use async-native libraries for database access (e.g., `asyncpg`, `motor`, `databases`), HTTP requests (`httpx`), and file operations (`aiofiles`). Alternatively, offload blocking calls to a thread pool (e.g., `loop.run_in_executor`).
• gotcha For features like caching, specific database integrations, or WebSocket functionality, additional libraries are often required beyond the basic `quart` install. For example, `quart-session` for sessions, `redis` or `python-memcached` for caching backends, or an async ORM.
  Fix: Consult Quart's documentation or community resources to identify and install the correct async-compatible libraries for desired functionality (e.g., `pip install quart-session redis`).

Install

• pip install quart Core installation
• pip install quart[dotenv] With .env file support

Imports

• Quart

  from quart import Quart

  Quart's API is Flask-compatible, but imports must be from `quart`.
• request

  from quart import request

  Use `quart.request` for the global request object within Quart applications.

Quickstart

A minimal 'Hello, World!' Quart application. Routes are defined using `@app.route` decorators on `async def` functions, returning a string. For production, it's recommended to run with an ASGI server like Hypercorn (e.g., `hypercorn app:app`).

from quart import Quart

app = Quart(__name__)

@app.route('/')
async def hello():
    return 'Hello, Quart!'

# To run this, save as app.py and execute: hypercorn app:app