Issue with automatic C++ wrapper during inheritance (to replace TPySelector)

In order to inherit from TSelector, old PyROOT provided the TPySelector class so that calls from C++ would be redirected to Python for those methods overridden in Python.

This should not be necessary in the new PyROOT, since cppyy implements the automatic generation of a C++ wrapper class during inheritance Python/C++ . Such class inherits from the C++ base class and redirects any call to Python for overridden methods in Python. Therefore, making the Python class inherit directly from TSelector should be sufficient.

However, when making a Python class inherit directly from TSelector, an error occurs. For example, the following code:

import ROOT

class MyPySelector(ROOT.TSelector):

    pass

throws

Traceback (most recent call last):

  File "simplets.py", line 3, in <module>

    class MyPySelector(ROOT.TSelector):

KeyError: 'fOutput'

fOutput is a protected data member of TSelector, which makes the C++ wrapper class generated during inheritance include using TSelector::fOutput;. Therefore, this issue is related to ROOT-10872, i.e. the problem with the using declarations.