Cache some properties

[Illviljan]

Cache some small properties that are rather slow to calculate but doesn't change that often.

Questions that needs to be resolved:

• [ ] Can these properties change during the lifetime of the class? If so the cache needs to be reset when that happens.

• [ ] Related to #3514
• [ ] Tests added
• [ ] Passes pre-commit run --all-files
• [ ] User visible changes (including notable bug fixes) are documented in whats-new.rst
• [ ] New functions/methods are listed in api.rst

Notes

• Mixin classes makes it difficult to cache properties. For example ndim in NdimSizeLenMixin cannot be easily be replaced with cache_readonly.

[github-actions[bot]]

Unit Test Results

         6 files           6 suites   53m 11s :stopwatch: 16 200 tests 14 465 :heavy_check_mark: 1 735 :zzz: 0 :x: 90 396 runs  82 221 :heavy_check_mark: 8 175 :zzz: 0 :x:

Results for commit 59bd433e.

:recycle: This comment has been updated with latest results.

[max-sixty]

Thanks for kicking this off @Illviljan .

My concern with this is that adding the _cache nullifies the benefits of slots. @keewis do you have any thoughts?

It also sounds like the speed-ups I was seeing might not be real. Probably we should have an ASV so there's a benchmark we're all looking at.

[Illviljan]

The case I'm optimizing is dataset interpolation with many variables. Although it's not the bottleneck there I halved the shape time from ~180ms to ~92ms with this change.

[max-sixty]

Resurrecting this, as discussed on the dev call.

Could we replace the pandas decorator with the one from the standard library? That may require adding __dict__ as a slot.

Then as long as the benchmarks still look good, there was consensus that we should merge.