Error messages need fixing too

Error messages updated

The /* Choose which subtype to return */ stuff, and declaration of prior1 and prior2, can move within the out == NULL branch now too

Do you want to wait on #9209 before finishing this off?

yeah let's wait

Rebased, and updated to use the recently defined PyArray_GetSubType.

I moved PyArray_GetSubType to ctors.c and added a declaration in ctors.h so it is visible across numpy C files.

(One slight difference in the new code is that I no longer use one of the input arrays as the "template" argument used in __array_finalize__ (last arg of PyArray_New/FromDescr). I think it is more correct now).

A little worried that not using one of the arrays as a template argument is a compatibility break, even if it wasn't necessarily good design before. Otherwise looks good.

Does this affect masked arrays in anyway, as the only built in subclass?

Yeah, I suspect this stops working:

>>> a = np.ma.array(np.eye(3))
>>> a._optinfo['x'] = 1
>>> np.dot(a, a)._optinfo
{'x': 1}

Which it seems people care about (#9279)

Yeah, you're right. I removed the last commit. (We also lose all the other info like the fillvalue).

The PR summary is now:

• Removed check for subtype of out argument
• moved (cut-n-paste) the subtype calculation into an else statement

Thanks!