#[pyattr]
#[pyclass(name = "pairwise")]
#[derive(Debug)]
struct PyItertoolsPairwise {
    ...
}

impl PyValue for PyItertoolsPairwise {
    fn class(_vm: &VirtualMachine) -> &PyTypeRef {
        Self::static_type()
    }
}

#[pyimpl(with(PyIter))]
impl PyItertoolsPairwise {
    #[pyslot]
    fn tp_new(
        cls: PyTypeRef,
        iterable: PyObjectRef,
        vm: &VirtualMachine,
    ) -> PyResult<PyRef<Self>> {
        ...
        PyItertoolsPairwise {
            ...
        }
        .into_ref_with_type(vm, cls)
    }
}

impl PyIter for PyItertoolsPairwise {
    fn next(zelf: &PyRef<Self>, vm: &VirtualMachine) -> PyResult {
        ...
    }
}