On Sun, 2026-03-29 at 12:49 +0000, Lucas Colley via NumPy-Discussion
wrote:
> Hi Sebastian,
>
> One thing this breaks is the following, which is part of SciPy's
> testsuite:
>
Hmmmpff, I guess it should not be all that many tests?! There isn't a
whole lot you can do with unitless datetimes at least, after all (i.e.
you can't even print them, IIRC -- timedelta is a bit better).
I can see two paths (besides reverting, which this doesn't seem enough
to me). We could improve the helpers here or even just add
`typecodes['Numeric']`. I.e. something new in `numpy.testing` that
actually lists a specific datetime with unit? Improving
`numpy.testing` in this way seems like a sensible thing anyway if we
have a good idea.
But the main fix is probably that I suspect can probably make
`np.dtype("m")` and `np.dtype("M")` specifically work returning a
default datetime unit [1].
(I am not actually not sure right now if NumPy has a real default, but
pandas has `ns`, so there is one, I guess.)
That would mean tests can be changed to just call `np.dtype(typecode)`
explicitly (if they otherwise change, `np.eye(, dtype=...)` already has
that behavior).
Cheers,
Sebastian
[1] `np.array([np.timedelta64(3, "ns")], dtype="m")` is different, and
that already seems to work right without giving a warning.
> ```
> @pytest.mark.parametrize("dtype", np.typecodes['All'])
> ...
> np.eye(2, dtype=dtype)
> ```
>
> Is there a recommended alternative for downstream libraries who want
> to test with ~all dtypes easily, but not all dtypes?
>
> https://github.com/scipy/scipy/actions/runs/23708171067/job/69063440694?pr=24921
>
> Cheers,
> Lucas
> ________________________________
> From: Sebastian Berg <[email protected]>
> Sent: 29 March 2026 11:37
> To: Discussion of Numerical Python <[email protected]>
> Subject: [Numpy-discussion] Deprecating unitless timedelta/datetime
>
> Hi all,
>
> I just merged a PR: https://github.com/numpy/numpy/pull/29619
> to deprecate unitless timdeldta/datetime64. This is a step in a
> direction
> that should be e.g. very helpful for pandas to make
> timedelta/datetimes
> less weird.
>
> That said, we didn't touch this for a long time, because it is also
> very hard to really understand how and if users might be impacted.
> So if you notice this, or maybe even think you may be mixing
> timedeltas
> with normal integers/floats a lot you may want to try this branch.
>
> This is a `DeprecationWarning`, so it shouldn't out-right break code
> in
> production.
>
> Note that there are also specific things we could try to make more
> gentle, even something niche like specifically allowing:
> `timdelta_arr == 0` (although `timedelta_arr.astype(bool)` should be
> a
> plausible replacement as well, I think).
> Or generally keep allowing `timedelta_arr + integer_arr`, etc. which,
> with this PR, I believe should give a warning.
>
> Cheers,
>
> Sebastian
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