[Python-Dev] Request for CPython 3.5.3 release

[Nick Coghlan]

On 2 July 2016 at 16:17, Ludovic Gasc <gmludo at gmail.com> wrote:
> Hi everybody,
>
> I fully understand that AsyncIO is a drop in the ocean of CPython, you're
> working to prepare the entire 3.5.3 release for December, not yet ready.
> However, you might create a 3.5.2.1 release with only this AsyncIO fix ?

That would be more work than just doing a 3.5.3 release, though - the
problem isn't with the version number bump, it's with asking the
release team to do additional work without clearly explaining the
rationale for the request (more on that below). While some parts of
the release process are automated, there's still a lot of steps to run
through by a number of different people:
https://www.python.org/dev/peps/pep-0101/.

The first key question to answer in this kind of situation is: "Is
there code that will run correctly on 3.5.1 that will now fail on
3.5.2?" (i.e. it's a regression introduced by the asyncio and
coroutine changes in the point release rather than something that was
already broken in 3.5.0 and 3.5.1).

If the answer is "No", then it doesn't inhibit the 3.5.2 rollout in
any way, and folks can wait until 3.5.3 for the fix.

However, if the answer is "Yes, it's a new regression in 3.5.2" (as in
this case), then the next question becomes "Is there an agreed
resolution for the regression?"

The answer to that is currently "No" - Yury's PR against the asyncio
repo is still being discussed.

Once the answer to that question is "Yes", *then* the question of
releasing a high priority fix in a Python 3.5.3 release can be
properly considered by answering the question "Of the folks using
asyncio, what proportion of them are likely to encounter problems in
upgrading to Python 3.5.2, and is there a workaround they can apply or
alternate approach they can use to avoid the problem?".

At the moment, Yury's explanation of the fix in the PR is
(understandably) addressed at getting the problem resolved within the
context of asyncio, and hence just describes the particular APIs
affected, and the details of the incorrect behaviour. While that's an
important step in the process, it doesn't provide a clear assessment
of the *consequences* of the bug aimed at folks that aren't themselves
deeply immersed in using asyncio, so we can't tell if the problem is
"Some idiomatic code frequently recommended in user facing examples
and used in third party asyncio based libraries may hang client
processes" (which would weigh in favour of an early 3.5.3 release
before people start encountering the regression in practice) or "Some
low level API's not recommended for general use may hang if used in a
particular non-idiomatic combination only likely to be encountered by
event loop implementors" (which would suggest it may be OK to stick
with the normal maintenance release cadence).

> If 3.5.2.1 or 3.5.3 are impossible to release before december,

Early maintenance releases are definitely possible, but the
consequences of particular regressions need to be put into terms that
make sense to the release team, which generally means stepping up from
"APIs X, Y, and Z broke in this way" to "Users doing A, B, and C will
be affected in this way".

As an example of a case where an early maintenance release took place:
several years ago, Python 2.6.3 happened to break both "from logging
import *" (due to a missing entry in test___all__ letting an error in
logging.__all__ through) and building extension modules with
setuptools (due to a change in a private API that setuptools was
monkeypatching). Those were considered significant enough for the
2.6.4 release to happen early.

> what are the
> alternative solutions for AsyncIO users ?
> 1. Use 3.5.1 and hope that Linux distributions won't use 3.5.2 ?

Linux distributions have mechanisms to carry patches (indeed,
selective application of patches is one of the main benefits of using
system packages over upstream ones), so any distro that rebases on
3.5.2 can be encouraged to add the fix once it lands regardless of
whether or not Larry approves an additional maintenance release
outside the normal cadence.

Cheers,
Nick.

-- 
Nick Coghlan   |   ncoghlan at gmail.com   |   Brisbane, Australia