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An ASGI web server, for Python.

Documentation:https://www.uvicorn.org

Uvicorn is an ASGI web server implementation for Python.

Until recently Python has lacked a minimal low-level server/application interface forasync frameworks. TheASGI specification fills this gap, and means we're now able tostart building a common set of tooling usable across all async frameworks.

Uvicorn supports HTTP/1.1 and WebSockets.

Install usingpip:

$ pip install uvicorn

This will install uvicorn with minimal (pure Python) dependencies.

$ 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 loopuvloop will be installed and used if possible.
• the http protocol will be handled byhttptools if possible.

Moreover, "optional extras" means that:

• the websocket protocol will be handled bywebsockets (should you want to usewsproto you'd need to install it manually) if possible.
• the--reload flag in development mode will usewatchfiles.
• windows users will havecolorama 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, inexample.py:

asyncdefapp(scope,receive,send):assertscope['type']=='http'awaitsend({'type':'http.response.start','status':200,'headers': [            (b'content-type',b'text/plain'),        ],    })awaitsend({'type':'http.response.body','body':b'Hello, world!',    })

Run the server:

$ uvicorn example:app

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 networkI/O such as dealing with slow HTTP requests.

A strength of the ASGI protocol is that it decouples the server implementationfrom the application framework. This allows for an ecosystem of interoperatingwebservers and application frameworks.

The first ASGI server implementation, originally developed to power Django Channels, isthe Daphne webserver.

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 usingdaphne instead.

$ pip install daphne$ daphne app:App

Hypercorn was initially part of the Quart web framework, beforebeing separated out into a standalone ASGI server.

Hypercorn supports HTTP/1.1, HTTP/2, and WebSockets.

It also supportsthe excellenttrio async framework, as an alternative toasyncio.

$ pip install hypercorn$ hypercorn app:App

Mangum is an adapter for using ASGI applications with AWS Lambda & API Gateway.

Granian is an ASGI compatible Rust HTTP server which supports HTTP/2, TLS and WebSockets.

Uvicorn isBSD licensed code.
Designed & crafted with care.
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