Introduction

Starlette is a lightweight ASGI framework/toolkit.

It is ideal for building high performance asyncio services, and supports both HTTP and WebSockets.

Requirements

Python 3.6+

Installation

$ pip3 install starlette

You'll also want to install an ASGI server, such as uvicorn, daphne, or hypercorn.

$ pip3 install uvicorn

Example

from starlette.applications import Starlette
from starlette.responses import JSONResponse
import uvicorn

app = Starlette()

@app.route('/')
def homepage(request):
    return JSONResponse({'hello': 'world'})

if __name__ == '__main__':
    uvicorn.run(app, host='0.0.0.0', port=8000)

Dependencies

Starlette does not have any hard dependencies, but the following are optional:

requests - Required if you want to use the TestClient.
aiofiles - Required if you want to use FileResponse or StaticFiles.
ujson - Optionally used for JSONResponse.

You can install all three of these with pip3 install starlette[full].

Framework or Toolkit

Starlette is designed to be used either as a complete framework, or as an ASGI toolkit. You can use any of its components independently.

from starlette.responses import PlainTextResponse


class App:
    def __init__(self, scope):
        self.scope = scope

    async def __call__(self, receive, send):
        response = PlainTextResponse('Hello, world!')
        await response(receive, send)

Run the App application in example.py:

$ uvicorn run example:App
INFO: Started server process [11509]
INFO: Uvicorn running on http://127.0.0.1:8000 (Press CTRL+C to quit)

Modularity

The modularity that Starlette is designed on promotes building re-usable components that can be shared between any ASGI framework. This should enable an ecosystem of shared middleware and mountable applications.

The clean API separation also means it's easier to understand each component in isolation.

Performance

Our testing shows that Starlette applications running under Uvicorn as one of the fastest Python frameworks available. As an example, application performance should roughly equal or out-perform Sanic.

For high throughput loads you should:

Make sure to install ujson.
Run using uvicorn, with access logging disabled.

Several of the ASGI servers also have pure Python implementations available, so you can also run under PyPy if your application code has parts that are CPU constrained.

Eg. uvicorn.run(..., http='h11', loop='asyncio')

— ⭐️ —

Starlette is BSD licensed code. Designed & built in Brighton, England.

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