uvicorn

An ASGI web server, for Python.

--- [![Build Status](https://github.com/Kludex/uvicorn/workflows/Test%20Suite/badge.svg)](https://github.com/Kludex/uvicorn/actions) [![Package version](https://badge.fury.io/py/uvicorn.svg)](https://pypi.python.org/pypi/uvicorn) [![Supported Python Version](https://img.shields.io/pypi/pyversions/uvicorn.svg?color=%2334D058)](https://pypi.org/project/uvicorn) [![Discord](https://img.shields.io/discord/1051468649518616576?logo=discord&logoColor=ffffff&color=7389D8&labelColor=6A7EC2)](https://discord.gg/RxKUF5JuHs) --- **Documentation**: [https://uvicorn.dev](https://uvicorn.dev) **Source Code**: [https://www.github.com/Kludex/uvicorn](https://www.github.com/Kludex/uvicorn) --- Uvicorn is an ASGI web server implementation for Python. Until recently Python has lacked a minimal low-level server/application interface for async frameworks. The [ASGI specification][asgi] fills this gap, and means we're now able to start building a common set of tooling usable across all async frameworks. Uvicorn supports HTTP/1.1 and WebSockets. ## Quickstart Install using `pip`: ```shell $ pip install uvicorn ``` This will install uvicorn with minimal (pure Python) dependencies. ```shell $ pip install 'uvicorn[standard]' ``` This will install uvicorn with "Cython-based" dependencies (where possible) and other "optional extras". In this context, "Cython-based" means the following: - the event loop `uvloop` will be installed and used if possible. - the http protocol will be handled by `httptools` if possible. Moreover, "optional extras" means that: - the websocket protocol will be handled by `websockets` (should you want to use `wsproto` you'd need to install it manually) if possible. - the `--reload` flag in development mode will use `watchfiles`. - windows users will have `colorama` installed for the colored logs. - `python-dotenv` will be installed should you want to use the `--env-file` option. - `PyYAML` will be installed to allow you to provide a `.yaml` file to `--log-config`, if desired. Create an application, in `example.py`: ```python async def app(scope, receive, send): assert scope['type'] == 'http' await send({ 'type': 'http.response.start', 'status': 200, 'headers': [ (b'content-type', b'text/plain'), ], }) await send({ 'type': 'http.response.body', 'body': b'Hello, world!', }) ``` Run the server: ```shell $ uvicorn example:app ``` --- ## Why ASGI? Most well established Python Web frameworks started out as WSGI-based frameworks. WSGI applications are a single, synchronous callable that takes a request and returns a response. This doesn’t allow for long-lived connections, like you get with long-poll HTTP or WebSocket connections, which WSGI doesn't support well. Having an async concurrency model also allows for options such as lightweight background tasks, and can be less of a limiting factor for endpoints that have long periods being blocked on network I/O such as dealing with slow HTTP requests. --- ## Alternative ASGI servers A strength of the ASGI protocol is that it decouples the server implementation from the application framework. This allows for an ecosystem of interoperating webservers and application frameworks. ### Daphne The first ASGI server implementation, originally developed to power Django Channels, is [the Daphne webserver][daphne]. It is run widely in production, and supports HTTP/1.1, HTTP/2, and WebSockets. Any of the example applications given here can equally well be run using `daphne` instead. ``` $ pip install daphne $ daphne app:App ``` ### Hypercorn [Hypercorn][hypercorn] was initially part of the Quart web framework, before being separated out into a standalone ASGI server. Hypercorn supports HTTP/1.1, HTTP/2, and WebSockets. It also supports [the excellent `trio` async framework][trio], as an alternative to `asyncio`. ``` $ pip install hypercorn $ hypercorn app:App ``` ### Mangum [Mangum][mangum] is an adapter for using ASGI applications with AWS Lambda & API Gateway. ### Granian [Granian][granian] is an ASGI compatible Rust HTTP server which supports HTTP/2, TLS and WebSockets. ---

Uvicorn is BSD licensed code.
Designed & crafted with care.
— 🦄 —

[asgi]: https://asgi.readthedocs.io/en/latest/ [daphne]: https://github.com/django/daphne [hypercorn]: https://github.com/pgjones/hypercorn [trio]: https://trio.readthedocs.io [mangum]: https://github.com/jordaneremieff/mangum [granian]: https://github.com/emmett-framework/granian