is_instance for 3rd party packages

[pravic]

refs #1914.

There's PyAny::is_instance::<T>(), however it's only for statically known types.

There's also PyType::is_instance(&obj) but it needs an instance of a checked type.

And, there's pyo3::import_exception! macro which looks like it can statically import a type even though it's for exceptions only.

What's the best approach for something like the following?

from mypackage import MyType

def is_my_type(obj: any) -> bool:
  return isinstance(obj, MyType)

By looking at import_exception! I've come up with this:

    fn is_my_type(obj: &PyAny) -> PyResult<bool> {
      let py = obj.py();
      let module = py.import("mypackage")?;
      let klass = module.getattr("MyType")?;
      let ty: &pyo3::types::PyType = klass.extract()?;
      ty.is_instance(obj)
    }

Is there anything better? Or it's idiomatic enough?

[birkenfeld]

I think that's as good as it gets. Of course, once you have a reference to the type object you can cache it somewhere when convenient.