Contexts

Quart, like Flask, has two contexts the application context and the request context. Both of these contexts exist per request and allow the global proxies current_app, request, etc… to be resolved. Note that these contexts are task local, and hence will not exist if a task is spawned by ensure_future or create_task.

The design principle of these contexts is that they are likely needed in all routes, and hence rather than pass these objects around they are made available via global proxies. This has its downsides, notably all the arguments relating to global variables. Therefore, it is recommended that these proxies are only used within routes so as to isolate the scope.

Application Context

The application context is a reference point for any information that isn’t specifically related to a request. This includes the app itself, the g global object and a url_adapter bound only to the app. The context is created and destroyed implicitly by the request context.

Request Context

The request context is a reference point for any information that is related to a request. This includes the request itself, a url_adapter bound to the request and the session. It is created and destroyed by the handle_request() method per request.

Websocket Context

The websocket context is analogous to the request context, but is related only to websocket requests. It is created and destroyed by the handle_websocket_request() method per websocket connection.

Tasks and contexts

Context is bound to a ContextVar and will be copied to tasks created from an existing task. To explicitly copy a context Quart provides the decorators copy_current_request_context() and copy_current_websocket_context() which can be used as so,

@app.route('/')
async def index():

    @copy_current_request_context
    async def background_task():
        method = request.method
        ...

    asyncio.ensure_future(background_task())
    ...

If you need to provide the request context in an asynchronous generator, use the quart.helpers.stream_with_context() decorator as discussed in Streaming responses:

@app.route('/')
async def index():

    @stream_with_context
    async def async_generator():
        async for data in request.body:
            yield data

    await consume_data(async_generator())
    ...

Note

These decorators must be used within an existing context, hence the background task is defined as a nested function.