How to register exceptions with custom attributes?

[ivany4]

Hello,

I'm not clear from the documentation how could one expose a C++ exception to Python that needs to have e.g. an additional readonly property. The output of py::register_exception() does not seem to have .def_property_readonly extension.

Problem #2: I wanted to write a custom translator using py::register_exception_translator, but documentation insists of using py::set_error inside, yet this function does not accept additional arguments beside the error message, so I would have no way of passing the custom value that should be exposed via that readonly property.

I'm also coming from #2884, but the workaround suggested there to use Python's exception instantiation would not solve the issue of passing a custom attribute into initializer.

Is it at all possible in pybind? Thanks!