too_late_unraisable.py is an example where PyErr_WriteUnraisable() is called very lated during Python finalization to be handled by user code. A destructor (__del__) fails on print() because the stream has been closed.

PyErr_WriteUnraisable() is called by _PyGC_CollectNoFail() at the *end* of PyImport_Cleanup(). At this point, the sys module has already been cleared, as all other modules. A custom sys.unraisablehook cannot be used, because sys has been called.