Which versions of Python should work for p4p?

[coretl]

p4p has just started giving me test failures on 3.6:

  _______________________________ test_asyncio_ioc _______________________________
  Traceback (most recent call last):
    File "/project/tests/test_asyncio.py", line 49, in test_asyncio_ioc
      assert await ctx.get(pre + ":AI") == 23.45
    File "/tmp/tmp.47L8V0mLtT/venv/lib/python3.6/site-packages/p4p/client/asyncio.py", line 122, in get
      return (await self._get_one(name, request=request))
    File "/tmp/tmp.47L8V0mLtT/venv/lib/python3.6/site-packages/p4p/client/asyncio.py", line 145, in _get_one
      cb = partial(asyncio.get_running_loop().call_soon_threadsafe, cb)
  AttributeError: module 'asyncio' has no attribute 'get_running_loop'

https://github.com/dls-controls/pythonSoftIOC/runs/6551492513?check_suite_focus=true#step:5:601

Docs state 2.7 or 3.4+, setup.py states 2.7+, but get_running_loop() is 3.7+. At DLS we don't use anything less than 3.7 with the epicscorelibs stack, so we would be happy to drop support for 3.6 and down on aioca, pythonSoftIOC, epicscorelibs and p4p. Not sure about other sites.

Alternatively we could revert to asyncio.get_event_loop() or your self.loop that you had before and keep 3.6.

Either way, I think we should change python_requires to be accurate: https://stackoverflow.com/questions/44660448/using-python-requires-to-require-python-2-7-or-3-2

Happy to submit a PR for whatever change you think is best.

[mdavidsaver]

This is arising from #80 and #82. Which, in my rush to put out a PVXS fix (epics-base/pvxs#27), I admit I forgot about. At minimum a change to compatibility should have triggered 4.1.0 (if not 5.0.0).

As for compatibility notation. This is complicated since there are two different compatibility ranges for the asyncio support, and the rest of P4P. After #82 the asyncio support is 3.7+, while the rest is 2.7, 3.5+ . The only way I could think to represent this in package metadata would be to move the asyncio support to another/new package, which would be a hassle by itself.

Alternatively we could revert to asyncio.get_event_loop() or your self.loop that you had before and keep 3.6.

Happy to submit a PR for whatever change you think is best.

I don't think that I have a preference. If you already have some changes, then by all means please share.

[mdavidsaver]

I notice that py3.6 has asyncio._get_running_loop(), which does most of the work.

https://github.com/python/cpython/blob/b74b1f36993a4e1700869133f3be13dd60ef4e40/Lib/asyncio/events.py#L638-L646

[coretl]

How concerned are you with backwards compatibility? Personally I'd be tempted to say we only support 3.7+ for everything, but I don't have any legacy systems on the epicscorelibs stack

[mdavidsaver]

For me, compatibility with FOSS is a question of effort. When it looks like too much effort, then I'll drop it absent some compelling reason. In this case, after noticing asyncio._get_running_loop() 3.6 support turns out not to be too difficult #86. However, I don't think you should feel compelled to support/test with the full range of versions which I currently support.

[mdavidsaver]

Also, I'm thinking about creating p4p 4.1.0, and "yanking" 4.0.1 from pypi.org. Thoughts/objections?

@AlexanderWells-diamond

[coretl]

3.6 support turns out not to be too difficult #86

Looks like a good solution

Also, I'm thinking about creating p4p 4.1.0, and "yanking" 4.0.1 from pypi.org. Thoughts/objections?

Sounds like a good idea to me.

[AlexanderWells-diamond]

I agree with coretl, I'm happy with that solution.

[mdavidsaver]

Ok, this is done https://pypi.org/project/p4p/#history

[AlexanderWells-diamond]

I can confirm p4p 4.1.0 now passes PythonSoftIOC's Python 3.6 CI:
https://github.com/dls-controls/pythonSoftIOC/actions/runs/2369933404