Unkown objects in docstring function signatures

I try to rely on mypy's stubgen (with recent improvements) to generate *.pyi files from Python classes generated by pybind11. It's almost perfect, though there are just a few things that needs a bit of polishing:

• iterator - when creating method with .def("some_func", [](some_type const &a) {return py::make_iterator(a.cbegin<elem_type>(), a.cend<elem_type>());}; then docstring is some_func() -> iterator. Type should be either Iterator (from typing) or even better, if it would be Iterator[elem_type]
• buffer - when binding method with signature add_buffer(py::buffer const &buf) the docstring is add_buffer(buffer: buffer). Is this buffer in Python2 and bytearray in Python3? Should stubgen alias bytearray as buffer in such cases?

Start with the mypy stubgen behavior described for pybind11-generated Python classes, comparing the iterator return signature and py::buffer parameter examples. No repository file or test is named, so first locate the signature-generation code and its tests. Done means the generated docstrings use appropriate iterator and buffer types, with regression coverage for both cases.