Even though __ipow__ might be documented to take a third argument, if you build an inplace_pow function using the C-API, you can only pass one argument to it.

You can see that in the attached screenshot.

The example class shown in the screenshot can be found here: https://github.com/Zuzu-Typ/Python-C-API-extension-template

With the little template I wasn't able to reproduce the crash, but I did reassure myself that the third object is neither Py_None nor NULL, by adding "if (obj2 == Py_None || obj2 == NULL) return NULL;" before line 469 in "template.c", because calling __ipow__ still returned an example_class instance, instead of an error message, as it should if it returned NULL.