starlette/responses.md at c902f98715a94536cd62c457c0c8583c5f1f413c

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Starlette includes a few response classes that handle sending back the appropriate ASGI messages on the send channel.

Response

Signature: Response(content, status_code=200, headers=None, media_type=None)

content - A string or bytestring.
status_code - An integer HTTP status code.
headers - A dictionary of strings.
media_type - A string giving the media type. eg. "text/html"

Starlette will automatically include a Content-Length header. It will also include a Content-Type header, based on the media_type and appending a charset for text types.

Once you've instantiated a response, you can send it by calling it as an ASGI application instance.

from starlette.responses import Response


async def app(scope, receive, send):
    assert scope['type'] == 'http'
    response = Response('Hello, world!', media_type='text/plain')
    await response(scope, receive, send)

Starlette provides a set_cookie method to allow you to set cookies on the response object.

Signature: Response.set_cookie(key, value, max_age=None, expires=None, path="/", domain=None, secure=False, httponly=False)

key - A string that will be the cookie's key.
value - A string that will be the cookie's value.
max_age - An integer that defines the lifetime of the cookie in seconds. A negative integer or a value of 0 will discard the cookie immediately. Optional
expires - An integer that defines the number of seconds until the cookie expires. Optional
path - A string that specifies the subset of routes to which the cookie will apply. Optional
domain - A string that specifies the domain for which the cookie is valid. Optional
secure - A bool indicating that the cookie will only be sent to the server if request is made using SSL and the HTTPS protocol. Optional
httponly - A bool indicating that the cookie cannot be accessed via Javascript through Document.cookie property, the XMLHttpRequest or Request APIs. Optional

Conversly, Starlette also provides a delete_cookie method to manually expire a set cookie.

Signature: Response.delete_cookie(key, path='/', domain=None)

HTMLResponse

Takes some text or bytes and returns an HTML response.

from starlette.responses import HTMLResponse


async def app(scope, receive, send):
    assert scope['type'] == 'http'
    response = HTMLResponse('<html><body><h1>Hello, world!</h1></body></html>')
    await response(scope, receive, send)

PlainTextResponse

Takes some text or bytes and returns an plain text response.

from starlette.responses import PlainTextResponse


async def app(scope, receive, send):
    assert scope['type'] == 'http'
    response = PlainTextResponse('Hello, world!')
    await response(scope, receive, send)

JSONResponse

Takes some data and returns an application/json encoded response.

from starlette.responses import JSONResponse


async def app(scope, receive, send):
    assert scope['type'] == 'http'
    response = JSONResponse({'hello': 'world'})
    await response(scope, receive, send)

UJSONResponse

A JSON response class that uses the optimised ujson library for serialisation.

Using ujson will result in faster JSON serialisation, but is also less careful than Python's built-in implementation in how it handles some edge-cases.

In general you probably want to stick with JSONResponse by default unless you are micro-optimising a particular endpoint.

from starlette.responses import UJSONResponse


async def app(scope, receive, send):
    assert scope['type'] == 'http'
    response = UJSONResponse({'hello': 'world'})
    await response(scope, receive, send)

RedirectResponse

Returns an HTTP redirect. Uses a 302 status code by default.

from starlette.responses import PlainTextResponse, RedirectResponse


async def app(scope, receive, send):
    assert scope['type'] == 'http'
    if scope['path'] != '/':
        response = RedirectResponse(url='/')
    else:
        response = PlainTextResponse('Hello, world!')
    await response(scope, receive, send)

StreamingResponse

Takes an async generator or a normal generator/iterator and streams the response body.

from starlette.responses import StreamingResponse
import asyncio


async def slow_numbers(minimum, maximum):
    yield('<html><body><ul>')
    for number in range(minimum, maximum + 1):
        yield '<li>%d</li>' % number
        await asyncio.sleep(0.5)
    yield('</ul></body></html>')


async def app(scope, receive, send):
    assert scope['type'] == 'http'
    generator = slow_numbers(1, 10)
    response = StreamingResponse(generator, media_type='text/html')
    await response(scope, receive, send)

Have in mind that file-like objects (like those created by open()) are normal iterators. So, you can return them directly in a StreamingResponse.

FileResponse

Asynchronously streams a file as the response.

Takes a different set of arguments to instantiate than the other response types:

path - The filepath to the file to stream.
headers - Any custom headers to include, as a dictionary.
media_type - A string giving the media type. If unset, the filename or path will be used to infer a media type.
filename - If set, this will be included in the response Content-Disposition.

File responses will include appropriate Content-Length, Last-Modified and ETag headers.

from starlette.responses import FileResponse


async def app(scope, receive, send):
    assert scope['type'] == 'http'
    response = FileResponse('statics/favicon.ico')
    await response(scope, receive, send)

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