The EchoClientProtocol example receives a "loop" argument, which is not used at all in the TCP example, and is used to create a future in the UDP example. In modern asyncio code the explicit loop arguments are no longer used since the loop can always be obtained with get_running_loop().

The proposed patch makes the UDP example consistent with the TCP one (by having the constructor accept the on_con_lost future) and removes the loop argument from both.

The was added originally by Victor and Yuri in c7edffdddd3 and 7c7605ff113

New changeset c717c73fa33a2f3591442059eaf6e7a673e2c725 by Miss Islington (bot) (Hrvoje Nikšić) in branch 'master':
bpo-38178: Don't explicitly pass "loop" to EchoClientProtocol. (GH-16159)
https://github.com/python/cpython/commit/c717c73fa33a2f3591442059eaf6e7a673e2c725

New changeset 701c4886bb0e19ad5ed8c8f556f65ab8597841e7 by Miss Islington (bot) in branch '3.7':
bpo-38178: Don't explicitly pass "loop" to EchoClientProtocol. (GH-16159)
https://github.com/python/cpython/commit/701c4886bb0e19ad5ed8c8f556f65ab8597841e7

Hrvoje, thanks for fixing this.

Next time, please involve the people who originally wrote the code.  They are both still active.  If they made mistakes, it helps them to know about it.  If they had a specific intent for the code example, it allows them to make sure the objectives are still being achieved.

New changeset 1cd6e926d30552056457820a682c1c361ee0f3ff by Miss Islington (bot) in branch '3.8':
bpo-38178: Don't explicitly pass "loop" to EchoClientProtocol. (GH-16159)
https://github.com/python/cpython/commit/1cd6e926d30552056457820a682c1c361ee0f3ff

Thanks Hrvoje!

Raymond, no problem; I guess I assumed that the authors are following the bug tracker (or have possibly moved on and are inactive).

I also had reason to believe the change to be non-controversial, since it is in line with Yury's own recommendations, e.g. from his 2018 EuroPython presentation (slide 14):

https://speakerdeck.com/1st1/asyncio-today-and-tomorrow

In any case, I am happy that the pull request has been processed and accepted so quickly - thanks everyone for the great work!

Raymond, sorry if I was so quick in applying.
The patch is very trivial and obvious.
I am pretty sure that Yuri and Victor approve it.

The PR doesn't fix a mistake, the code is still valid.
But we all changed our mind what is the loop role, should it be explicitly passed everywhere or not, etc.

At the time of the example creation explicit loop was safer, after Python 3.5.3 bugfx release the implicit loop became the idiomatic solution.

We use the implicit loop everywhere, 3.8 raises DeprecationWarning for passing the loop into certain API calls.
The PR just changes the example to follow our own recommendations.

> In modern asyncio code the explicit loop arguments are no longer used since the loop can always be obtained with get_running_loop().

Yeah, the trend changed. Around Python 3.4, passing explicitly loop was preferred for best performances.

Since that time, the code to get the current loop has been optimized, and the new trend is to make the loop implicit to make the code more readable.

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When I wrote the doc, self.loop.stop() was called explicitly:

https://docs.python.org/3.5/library/asyncio-protocol.html#tcp-echo-client-protocol

It seems like the example has been modified to add a new "on_con_lost" Future.

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Anyway, thanks Hrvoje Nikšić for your contribution ;-)