DEP: Actually deprecate np.dtype('O8')

[eric-wieser]

The code before tried to:

• Deprecate np.dtype('O8')
• Silently allow loading pickles containing 'O8'

But actually due to a logic bug:

• Silently allowed np.dtype('O8')
• Deprecated loading pickles containing 'O8'

Since we already deprecated the pickles for 8 years by accident, we may as well just deprecate both uses now.

[seberg]

LGTM, will probably just commit the suggestion and merge myself later. Fun typo, just shows that even simple code is better with tests :).

[seberg]

Hmm, a bit more fallout than I thought, there is an actual tests unpickling an O8 dtype that fails currently.

[eric-wieser]

Hmm, a bit more fallout than I thought, there is an actual tests unpickling an O8 dtype that fails currently.

I was under the impression that when unpickling the warning was already emitted. Am I mistaken?

[seberg]

I am as confused as you are, but round tripping tests for npz are failing for example:
https://dev.azure.com/numpy/numpy/_build/results?buildId=8798&view=logs&j=25bb66cf-4a16-533e-490c-8da4b5a3ec04&t=97446ee6-ebce-5662-24e5-f82eed312005&l=802

Probably this is not array but the single dtype pickle. However, the roundtripping should certainly work, so I guess the state setting may be off, since it should not be storing O8 to begin with?

[eric-wieser]

Here's the issue:

>>> np.dtype(object).__reduce__()
(numpy.dtype, ('O8', False, True), (3, '|', None, None, None, -1, -1, 63))

[anirudh2290]

can we also get rid of extern declaration in conversion_utils.h

There are still failing tests

[mattip]

There are still failing tests

[charris]

@eric-wieser Ping. Do you want to keep this open? You have a bunch of PRs, it would be helpful if you looked through them and decided which you would like to keep open.