`_threadmodule` does not check for `NULL` after `PyType_GetModuleByDef` calls

[sobolevn]

Bug report

PyType_GetModuleByDef can return NULL:

cpython/Objects/typeobject.c

Lines 4640 to 4645 in fd49e22

	PyErr_Format(
	PyExc_TypeError,
	"PyType_GetModuleByDef: No superclass of '%s' has the given module",
	type->tp_name);
	return NULL;
	}

I think that right now this is a hypothetical issue, because in practice NULL will never be returned for these samples. But, all other similar places do check for NULL. I guess that adding a check won't hurt. And in the future, if something changes - we would be safe.

Samples:

cpython/Modules/_threadmodule.c

Lines 903 to 904 in fd49e22

	PyObject *module = PyType_GetModuleByDef(type, &thread_module);
	thread_module_state *state = get_thread_state(module);

cpython/Modules/_threadmodule.c

Lines 1044 to 1045 in fd49e22

	PyObject *module = PyType_GetModuleByDef(Py_TYPE(self), &thread_module);
	thread_module_state *state = get_thread_state(module);

cpython/Modules/_threadmodule.c

Lines 1096 to 1097 in fd49e22

	PyObject *module = PyType_GetModuleByDef(Py_TYPE(self), &thread_module);
	thread_module_state *state = get_thread_state(module);

Linked PRs

• gh-114414: Check for NULL after PyType_GetModuleByDef in _threadmodule #114415

[erlend-aasland]

For similar cases (retrieve module state in an extension module), we normally use assert.