Restrict a bond dictionary to self.

        Args:
            bond_dict (dict): Look into :meth:`~chemcoord.Cartesian.get_bonds`,
                to see examples for a bond_dict.

        Returns:
            bond dictionary

def restrict_bond_dict(self, bond_dict):
        """Restrict a bond dictionary to self.

        Args:
            bond_dict (dict): Look into :meth:`~chemcoord.Cartesian.get_bonds`,
                to see examples for a bond_dict.

        Returns:
            bond dictionary
        """
        return {j: bond_dict[j] & set(self.index) for j in self.index}