def get_axis_num(self, dim: Union[Hashable, Iterable[Hashable]]
                     ) -> Union[int, Tuple[int, ...]]:
        """Return axis number(s) corresponding to dimension(s) in this array.

        Parameters
        ----------
        dim : str or iterable of str
            Dimension name(s) for which to lookup axes.

        Returns
        -------
        int or tuple of int
            Axis number or numbers corresponding to the given dimensions.
        """
        if isinstance(dim, Iterable) and not isinstance(dim, str):
            return tuple(self._get_axis_num(d) for d in dim)
        else:
            return self._get_axis_num(dim)