Re: Proposal: Adding finfo support for user-defined DTypes

Hi Swayam,

If we have a slot, I'd prefer it to be more general.  However, also two
other thoughts:

1) Might it be possible to do this via subclassing? I.e., if one creates
   a floating type, one subclasses a FloatingDTypeMeta that has some
   slots particularly logical for floats, such as the .finfo information
   (it could then be numbers rather than a function), and perhaps also
   how NaN (and +/-inf?) are encoded?

2) In a different direction, might it be worthwile considering going the
   other way, for a DType to register a function that provides the
   required information with `np.finfo`?  That avoids increasing number
   of slots on the DType, and is similar to how a DType also has to
   register itself for the casting, ufuncs, etc.  (I've been suggesting
   that similarly for (arg)sort we don't add slots but rather a
   registration mechanism; see discussion in
   https://github.com/numpy/numpy/pull/29737).  Conceptually, this could
   be as simple as adding to a `dict` keyed by dtype with the value
   being another dict that gives `precision`, `eps`, etc.

All the best,

Marten

Swayam Singh via NumPy-Discussion <[email protected]> writes:

> Hi all,
>
> Following recent discussion, I wanted to summarize the current status of extending `np.finfo` to user-defined DTypes.
>
> At present, there is no way for user DTypes to provide their own `finfo` information (e.g., precision, bits, eps) [issue #27231](https://github.com/numpy/numpy/issues/27231).
> To address this, [PR #29763](https://github.com/numpy/numpy/pull/29763) proposes adding a new `NPY_DT_get_finfo` slot so that user-defined floating DTypes can expose this metadata.
> One open question from review is whether this should remain specific to `finfo`, or if we should generalize the mechanism so that other numeric types (e.g., integers via `iinfo`) could also expose their own limits.
>
> I’d appreciate feedback on whether we should:
>
> * start with `finfo` support for floating user DTypes only, or
> * aim for a more general interface covering both `finfo`, `iinfo`, and potentially other numeric limits.
>
> Best,
> Swayam Singh
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