async_context.py

import inspect
import asyncio
from async_generator import asynccontextmanager

class Response:
    def __init__(self, body):
        self._body = body

    async def body(self):
        return self._body


class Request:
    def __init__(self, url, **kwargs):
        self.url = url
        self.kwargs=  kwargs

    async def __aenter__(self):
        print(f"Request {self.url} with {self.kwargs}")
        return Response(f"Response to {self.url}")

    async def __aexit__(self, *args, **kwargs):
        pass

@asynccontextmanager
async def request(url, kwargs):
    if inspect.isawaitable(kwargs):
        kwargs = await kwargs

    kwargs.setdefault('headers', {}).update(dict(UserAgent='test'))

    async with Request(url, **kwargs) as rsp:
        yield rsp


def authorized_request(url):
    async def get_kwargs():
        return dict(headers=dict(Auth='foobar'))

    return request(url, kwargs=get_kwargs())

async def get_simple():
    async with authorized_request("/simple") as rsp:
        return await rsp.body()

def get_full():
    return authorized_request("/schedule")

async def main():
    print(await get_simple())

    async with get_full() as rsp:
        print(await rsp.body())


loop = asyncio.get_event_loop()
loop.run_until_complete(main())