Regression in deriving from C++ classes with protected data members with Python 3.13

[guitargeek]

Reproducer:

import cppyy

cppyy.cppdef("""

class MyBaseClass{
public:
   virtual ~MyBaseClass() = default;
protected:
   int _data = 0;
};

""")

class MyDerivedClass(cppyy.gbl.MyBaseClass):
    pass

The error:

Traceback (most recent call last):
  File "reproducer.py", line 14, in <module>
    class MyDerivedClass(cppyy.gbl.MyBaseClass):
        pass
KeyError: '_data'

[guitargeek]

Can be fixed like this: root-project/root#16851

[wlav]

The example above doesn't fail for me.

It's also not clear to which part you are referring in the above, but if this:

#if PY_VERSION_HEX < 0x30d00f0
         PyObject* pyf = PyMapping_GetItemString(disp_dct, (char*)name.c_str());
#else
         PyObject* pyf = nullptr;
         PyMapping_GetOptionalItemString(disp_dct, (char*)name.c_str(), &pyf);
#endif

then all that does is suppress the exception, not solve the issue. It's also not Py3.13 specific.

That is, in your case, does this work (it does for me):

class MyDerivedClass(cppyy.gbl.MyBaseClass):
    def gime(self):
        return self._data

m = MyDerivedClass()
print(m.gime())

B/c if only the error is suppressed with the "fix", then the above will still fail.