Client tracing example emits deprecation warning

[jcugat]

Long story short

Example of client tracing in the documentation emits a deprecation warning.

Expected behaviour

Execution without any deprecation warning.

Actual behaviour

$ python -Wd test.py
test.py:7: DeprecationWarning: client.loop property is deprecated
  trace_config_ctx.start = session.loop.time()
test.py:11: DeprecationWarning: client.loop property is deprecated
  elapsed = session.loop.time() - trace_config_ctx.start
Request took 0.2158021649811417

Steps to reproduce

The example is taken from https://docs.aiohttp.org/en/stable/client_advanced.html#client-tracing

import asyncio

import aiohttp


async def on_request_start(session, trace_config_ctx, params):
    trace_config_ctx.start = session.loop.time()


async def on_request_end(session, trace_config_ctx, params):
    elapsed = session.loop.time() - trace_config_ctx.start
    print("Request took {}".format(elapsed))


async def run():
    trace_config = aiohttp.TraceConfig()
    trace_config.on_request_start.append(on_request_start)
    trace_config.on_request_end.append(on_request_end)
    async with aiohttp.ClientSession(trace_configs=[trace_config]) as client:
        await client.get("http://example.com/some/redirect/")


if __name__ == "__main__":
    loop = asyncio.get_event_loop()
    loop.run_until_complete(run())
    loop.close()

Your environment

Aiohttp as a client.

$ python -V
Python 3.6.8
$ pip freeze | grep aiohttp
aiohttp==3.5.4

Possible solutions

Should the session.loop not emit a deprecation warning? (a.k.a is this a bug?). Or should the example use asyncio.get_event_loop() instead?

[asvetlov]

The second: use asyncio.get_event_loop() or even better asyncio.get_running_loop()

[jcugat]

Got it, will open a PR fixing the documentation then.

[asvetlov]

Fixed by #3965