Consider an example:

if (((PyObject*)obj)->data==Py_None) {111;}if (Py_None== ((PyObject*)obj)->data) {111;}

Afterupgrade_pythoncapi.py I got:

#include"pythoncapi_compat.h"if (((PyObject*)obj)->Py_IsNone(data)) {111;}if (Py_None== ((PyObject*)obj)->data) {111;}

Real world example:
https://github.com/aleaxit/gmpy/blob/eb8dfcbd84abcfcb36b4adcb0d5c6d050731dd75/src/gmpy2_xmpz_misc.c#L237

I'm not sure if this is a bug. This kind of issues is not easy to avoid, using regexps for code transformations. Have you considered to use something like thepycparser?

Thanks for the project.