Add LTS to SPEC 0

[jarrodmillman]

Fix #190. Fix #386. See scikit-learn/scikit-learn#30888 (comment).

Todo:

• Get scikit-learn feedback
• Get approval from all core projects that currently endorse SPEC 0
• update spec-0000/SPEC0_versions.py

[bsipocz]

I really like phrasing this as LTS, it feels to be a nice extension and compromise!

I haven't looked in into the test failures, obviously the approval is not for any potentially relevant failures.

[virchan]

I think what's outlined in LTS is consistent with what scikit-learn is doing in scikit-learn/scikit-learn#30888.

So I would like to ping @lesteve and @lucascolley to see if they have any thoughts or input.

[mdhaber]

The first sentence is that all projects should adopt a common policy. This goes against that, so I think we should acknowledge the discrepancy in some way. If we do not recommend one over the other, the first sentence might change to be "adopt one of two time-based poicies...". If we have a preference for the first but recognize the need for the other, we might say something to that effect here.

[mdhaber]

Suggestions about the new text are inline.

If we were modifying other text:

• I don't understand the connection between the timeframe over which new releases support old dependency versions and the timeframe over which a given (feature) release will get bug fix releases. I think the SPEC would be more focused if it only mentions the former.
• The "Ecosystem Adoption" and "Implementation" sections are empty. Is that desirable?
• The background and motivation appears at the end, after the policy itself. Was that intentional?
• The SPEC only mentions limiting support duration as a motivation. Does it also recommend providing at least a certain amount of time - just not much more?

But if the intent is to address only LTS here, feel free to hide this comment as "off topic".

[lucascolley]

I agree with Matt's comments, but otherwise this looks like a useful change!

[lesteve]

I am a bit confused about this. This seems like one more year of support for the non-LTS recommendation but I may be missing some context ...

For Python (yearly release cadence), "3 years after the next version is released" means "4 years since the initial release".

The changes in chart.md seem to agree with this "one more year of Python support".

[mdhaber]

Good point. When talking about this correction of the logic, we've discussed only support for core package dependencies like NumPy. Since the time between releases is typically 6 months, we've actually discussed that we could drop support for an old version 18 months after the next version release. Since the release cadence of Python is annual, we could keep the same nominal time by making this two years after the next release and still keep the same nominal schedule.

So one option is to change these numbers to 1.5 and 2. We could make both 2 years for simplicity, but indeed, that would change the nominal support time for core dependencies.

[stefanv]

Observations from discussions here at EuroSciPy:

• The "after the next release" phrasing is confusing.
• With the "after the next" change, doesn't this immediately grow the window, so that the LTS version is now two years longer?
• As a maintainer, it's useful to think in terms of "oldest supported version": i.e., "minimum version of Python should be a bit older than 3 yrs", then look up release dates and find that version of Python. Or, to phrase differently: at the point in time where you need the information, you need to look back, so the forward-looking formulation is confusing.
• May be worth formulating this both in terms of support windows and "today - 3 years, what was released" to match different intuitive approaches. Some people like the graphic approach as-is.
• Can we also visualize LTS on existing plot by shifting the red line?
• Stretch goal: would be nice to have a JS version that fetches release information from PyPi and generates the plot dynamically.

[lucascolley]

Can we also visualize LTS on existing plot by shifting the red line?

A toggle or tab for this would be nice!