Convert this variable to a pandas.Index

def to_index(self):
        """Convert this variable to a pandas.Index"""
        # n.b. creating a new pandas.Index from an old pandas.Index is
        # basically free as pandas.Index objects are immutable
        assert self.ndim == 1
        index = self._data.array
        if isinstance(index, pd.MultiIndex):
            # set default names for multi-index unnamed levels so that
            # we can safely rename dimension / coordinate later
            valid_level_names = [name or '{}_level_{}'.format(self.dims[0], i)
                                 for i, name in enumerate(index.names)]
            index = index.set_names(valid_level_names)
        else:
            index = index.set_names(self.name)
        return index