I am trying to define a type in C, that derives from PyTypeObject.

I want to override tp_clear. To do so properly, I should call base type's tp_clear and have it perform its cleanup steps. PyTypeObject has a tp_clear implementation: subtype_clear. Problem is, it assumes the instance it gets is of a type, that does not override PyTypeObject's tp_clear, and behaves incorrectly in 2 ways:

1) it does not perform the usual cleanup, because in this code
base = type;
while ((baseclear = base->tp_clear) == subtype_clear)

the loop condition is immediately false, as my types overrode tp_clear

2) later on it calls baseclear on the same object. But because of the loop above baseclear actually points to my type's custom tp_clear implementation, which leads to reentry to that function (basically a stack overflow, unless there's a guard against it).