pywin32 has, since the 90s, used c++ to "inherit" from a PyObject in some cases. In short, it ends up something like:

class MyObject : public PyObject {  virtual void some_helper();}

With a layout like this, areinterpret_cast between aMyObject * and aPyObject * will create invalid pointers.

Consider something like the following:

void MyObject::some_helper() {  Py_DECREF(this);}

This ends up being a macro which uses_PyObject_CAST on the param passed toPy_DECREF.In 3.10, this uses a traditional "c" cast , butin 3.11 it turned into areinterpret_cast. In the above example, this causesPy_DECREF to be called with an invalidPyObject * - which typically doesn't crash at the time, but instead corrupts memory causing a difficult to diagnose crash some time later.

Changing the code to use explicitstatic_cast<>, or the old-school(PyObject *) cast makes things work, but it would be error prone as it would be easy to miss places where it's used via non-obvious nested macros. It also shouldn't be necessary to make this kind of change - c++ code which has worked for this long should continue to work.