Drop Python 3.5?

[arporter]

The notebook tests are failing for Python 3.5. Possibly this is because Jupyter has dropped support for Python 3.5 (jupyter/notebook#5962). Apparently 3.5 was EOL last September.

As discussed at jupyter/notebook#5961 (comment)), we could choose to pin the version of Jupyter we use but I think a better option is to drop 3.5.

[arporter]

For now, I've made the success of the Python 3.5 tests an optional requirement before merging a branch to master.

[hiker]

I'm ok with dropping 3.5 (Intel OneAPI comes with python 3.7.9, and I am using 3.8).

[sergisiso]

Even if Python 3.5 is not marked as required now, when it fails it cancels the other tests and make the whole CI not pass.

[rupertford]

If we are going to do this then it should be made clear in the documentation that it does not work. Also, what version of Python3 do the Met Office use and what version is in the LTS versions of linux? If 3.5 is still a standard version anywhere then I don't think we should drop it. I also thought that Sergi found that this problem had gone away (and I've not noticed it yet) - obviously not?

[TeranIvy]

We're using 3.6.8 in LFRic, so from our point of view it makes sense to replace 3.5 testing with 3.6.

[arporter]

Apparently 3.5 is shipped with Ubuntu 16.0.4 which (I've just learned) reaches EOL this month! Therefore, it may be premature to drop support for it. Strictly speaking, we just wouldn't be running the test suite for it any more - we could still support it if a user appeared who needed it.

[arporter]

Suddenly this problem has gone away again! I've delved in the logs for the tests and there are differences in the dependencies that are being installed:

$ diff working_list.txt broken_list.txt 
< decorator-5.0.6-py3-none-any.whl
> decorator-5.0.5-py3-none-any.whl
< jupyter_client-6.1.12-py3-none-any.whl
> jupyter_client-6.1.13-py3-none-any.whl
> nest_asyncio-1.5.1-py3-none-any.whl

[arporter]

Anyway, we can close this for the time being.

[arporter]

@LonelyCat124 is getting failures again with 3.5 which is now a year past its EOL. 3.6 reaches EOL this year too. I propose we drop 3.5...

[arporter]

and @LonelyCat124 also points out that 3.10 is due in 5 days!

[LonelyCat124]

Ubunbu 18.04 LTS end their "Hardware and maintenance updates" 6/2022, and ships with Python 3.6 as their default Python version, so I've bumped 3.5 up to 3.6 in #1415 as discussed with Andy

[arporter]

Flake8 is now failing with 3.5 and I can see no reason (given the above discussion) not to switch from 3.5 to 3.6 so I'll open a PR.

[sergisiso]

We could also consider bumping 3.8 to 3.10 in GHA, so we check with the oldest and latest stable versions.

[arporter]

Yes, I'd be happy with that. Any objections from @TeranIvy, @rupertford or @hiker ?

[hiker]

OK with me.

[arporter]

Reopening as I've hit trouble with the fact that we pin the version of jsonschema in setup.py and there's a TODO there for this issue (naughty us missing that).