PyType_GenericAlloc() cannot traverse the object since the object members are not initialized yet. For example, dict_traverse() can only be called when PyDict_New() completes.

A different approach would be to:

* (1) Add PyType_AllocNoTrack(), use it in built-in types, and call _PyObject_GC_TRACK() on the instance once it is fully initialized.
* (2) Modify PyType_GenericAlloc() to use a new variant of _PyObject_GC_TRACK() which will not traverse the instance.
* (3) Modify _PyObject_GC_TRACK() to traverse the instance.

In short, PyType_GenericAlloc() cannot be modified for backward compatibility.

Moreover, _PyObject_GC_TRACK() should only be used inside Python internals, since it's part the internal C API.