Allow user defined exceptions to have docstrings

[mejrs]

For #2016

[mejrs]

I don't know why this error occurs only on certain platforms:
Error: PyErr { type: <class 'NameError'>, value: NameError("name 'str' is not defined"), traceback: Some(<traceback object at 0x0000022BD1373448>) }.

while running

/// # fn main() -> PyResult<()> {
/// #     Python::with_gil(|py| -> PyResult<()> {
/// #         let fun = wrap_pyfunction!(raise_myerror, py)?;
/// #         let globals = pyo3::types::PyDict::new(py);
/// #         globals.set_item("MyError", py.get_type::<MyError>())?;
/// #         globals.set_item("raise_myerror", fun)?;
/// #
/// #         py.run(
/// # "try:
/// #     raise_myerror()
/// # except MyError as e:
/// #     assert e.__doc__ == 'Some description.'
/// #     assert str(e) == 'Some error happened.'",
/// #             Some(globals),
/// #             None,
/// #         )?;
/// #
/// #         Ok(())
/// #     })
/// # }

[davidhewitt]

Sorry it took me a while to get to this, thanks for implementing! Got a few ideas and comments r.e. the new_type stuff

[mejrs]

I have combined the functions and made it return Result<Py<PyType>>. I think this is good to go after the 1.57 changes merge.

[davidhewitt]

Sorry for the catastrophically slow reviewing. Looks great to me! Just needs rebasing and a CHANGELOG entry :)

[mejrs]

Sorry for the catastrophically slow reviewing. Looks great to me! Just needs rebasing and a CHANGELOG entry :)

Should be good to go now :)

[davidhewitt]

Perfect, thanks again!

[9999years]

Any chance we could cut a release with this feature? I forked pyo3 to add this but it's already here, just unreleased.

[davidhewitt]

@9999years please follow #2079 - we're getting close to last piece we want to complete before next release lands. You might be able to use a git dependency in the meanwhile?