have PyErr's Debug implementation call traceback.format()

[nicolasavru]

Could PyErr's Debug implementation call traceback.format()? Something like .field("traceback", &self.traceback(py).map(|tb| tb.format()))

Err(PyErr { type: <class 'SomeError'>, value: SomeError('some message'), traceback: Some(<traceback object at 0x53e96c8c6300>) }) isn't especially helpful and there doesn't seem to be a convenient way of getting a string (e.g., to pass to a logging library) of a PyErr with a traceback. I could write a function to do that, but it's easy to forget to call a custom function.