List of the side-chain atoms (R-group).

        Notes
        -----
        Returns empty list for glycine.

        Returns
        -------
        side_chain_atoms: list(`Atoms`)

def side_chain(self):
        """List of the side-chain atoms (R-group).

        Notes
        -----
        Returns empty list for glycine.

        Returns
        -------
        side_chain_atoms: list(`Atoms`)
        """
        side_chain_atoms = []
        if self.mol_code != 'GLY':
            covalent_bond_graph = generate_covalent_bond_graph(
                find_covalent_bonds(self))
            try:
                subgraphs = generate_bond_subgraphs_from_break(
                    covalent_bond_graph, self['CA'], self['CB'])
                if len(subgraphs) == 1:
                    subgraphs = generate_bond_subgraphs_from_break(
                        subgraphs[0], self['CD'], self['N'])
                if len(subgraphs) == 2:
                    for g in subgraphs:
                        if self['CB'] in g:
                            side_chain_atoms = g.nodes()
                            break
            except:
                warning_message = "Malformed PDB for Residue {0}: {1}.".format(
                    self.id, self)
                if 'CB' in self.atoms.keys():
                    side_chain_atoms.append(self['CB'])
                    warning_message += " Side-chain is just the CB atom."
                else:
                    warning_message += " Empty side-chain."
                warnings.warn(warning_message, MalformedPDBWarning)
        return side_chain_atoms