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BUG: restore ndarray.conjugate() for legacy user-defined dtypes - #31936
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numpygh-31264 rewrote PyArray_Conjugate to dispatch to the conjugate ufunc only when the DType defines an `imag_meth` slot, dropping the explicit `PyArray_ISUSERDEF` route. Legacy user dtypes have no `imag_meth` and are not flagged numeric, so `arr.conjugate()` began raising "cannot conjugate non-numeric dtype" in 2.5.0, even when a conjugate ufunc loop is registered (e.g. numpy-quaternion). Restore the legacy user-dtype route so these dtypes dispatch to the ufunc as before, while leaving the new-style view/numeric behavior intact. Closes numpy#31754
ngoldbaum
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LGTM I just think you accidentally a word in the comment.
Co-authored-by: Nathan Goldbaum <[email protected]>
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Co-authored-by: Mike Boyle <[email protected]> Co-authored-by: Nathan Goldbaum <[email protected]>
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BUG: restore ndarray.conjugate() for legacy user-defined dtypes (#31936)
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Kept the old PR. The problem is that while legacy user dtypes can implement things and even make themselves "Numeric" in theory, they aren't in practice and they should probably just keep trying the ufunc...
However, unlike the old PR. However, at least open a path forward if the numeric flag is set (possible via new "backport" API) and maybe we can even provide a nicer way to set it (not that you can't just do it in theory...).
CC @moble
Closes gh-31754