BUG: incorrect temp elision for new-style (NEP 43) user-defined dtypes (#31193)#31329
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numpy#31193) Co-authored-by: Maarten Baert <[email protected]> Co-authored-by: Sebastian Berg <[email protected]>
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Backport of #31193.
PR summary
can_elide_temp()intemp_elide.cincorrectly identifies new-style user-defined dtypes as numeric types eligible for in-place buffer reuse. For large arrays this silently rewritesa*a + b*binto(a*a) += (b*b), which raises aTypeErrorwhen the result dtype of the in-place add does not match the pre-allocated buffer.I encountered this bug while implementing a custom fixed-point dtype, which automatically increases its bit width on every operation as required to avoid overflow. Since addition increases the bit width by one, attempting to reuse the temporary buffer results in an incompatible destination dtype being provided to the
addufunc and raises aTypeError.The root cause is that
PyArray_ISNUMBERevaluates totruefor new-style user dtypes since it checks(type) <= NPY_CLONGDOUBLEandtype_num = -1for these types.This could be fixed either in
PyArray_ISNUMBER(probably more correct, but may have unexpected side effects) or with a minimal extra check incan_elide_temp(the approach used by the PR). Let me know if you'd like me to fixPyArray_ISNUMBERinstead.AI Disclosure
This bug was identified and fixed by Claude Sonnet 4.6, and then reviewed by me.
Full AI-generated explanation: https://gist.github.com/MaartenBaert/7540176c4005d26a0b292baefbec8519