def _selector_get_type_feat(self, i, typefeats_i=None):
        """Get information only from selector.

        Parameters
        ----------
        i: int, list or np.ndarray
            the index information.
        typefeats_i: list, tuple or None (default=None)
            the selector information of all the selections we have to do
            in that process for each element `i`.

        Returns
        -------
        typefeats_i: tuple or list
            the selectors for the features of the elements `i`.
        typefeats_nei: tuple or list
            the selectors for the features of the neighs of elements `i`.
        typefeats_desc: tuple or list
            the selection of the features and descriptormodel to compute the
            descriptor from desc_i and desc_neighs.

        """
        selector_i = format_selection(self.selector[i])
        typefeats_i, typefeats_nei, typefeats_desc = selector_i
        #        if type(i) == int:
        #            typefeats_i, typefeats_nei, typefeats_desc = self.selector[i]
        #        else:
        #            typefeats_i, typefeats_nei, typefeats_desc = [], [], []
        #            selectors_i = self.selector[i]
        #            print selectors_i
        #            for j in range(len(i)):
        #                typefeats_i.append(selectors_i[j][0])
        #                typefeats_nei.append(selectors_i[j][1])
        #                typefeats_desc.append(selectors_i[j][2])
        return typefeats_i, typefeats_nei, typefeats_desc
    def _selector_get_type_ret(self, i, typeret_i=None):
        """Get information only from selector.

        Parameters
        ----------
        i: int
            the element id.
        typeret_i: tuple, np.ndarray or None (default)
            the selector of the retrievers we want to use.

        Returns
        -------
        typeret_i: int
            the retriever we want to use.
        out_ret: int
            the out retriever we want to use.

        """
        selection = format_selection(self.selector[i])
        typeret_i, out_ret = selection
        return typeret_i, out_ret