Is third input to createIndex really a pointer?

[Infinity]

The internal pointer is used by the model to associate the index with the internal data structure (from the docs).

It seems like you're doing something like the Simple Tree Model Example: http://qt-project.org/doc/qt-4.8/ite...treemodel.html
Here the internal pointer points to a TreeItem instance which holds data for the index and also a pointer to the parent of the index (which points to another TreeItem instance of course). This pointer is used as internal pointer when creating the parent index.

Given that I am working in Python, which does not use pointers

Correct, in Python you don't use pointers (all values are references). Maybe it would make more sense to talk about "internal objects" here.

[neuronet]

Maybe this is a case where translation of documentation to Python hasn't been as smooth because we don't use pointers

(Note I just added to original post: I x-posted this to stack overflow)