def categories(self):
        """Returns the categories of `Ligands` in `LigandGroup`."""
        category_dict = {}
        for ligand in self:
            if ligand.category in category_dict:
                category_dict[ligand.category].append(ligand)
            else:
                category_dict[ligand.category] = [ligand]
        return category_dict
def categories ( self ) : category_dict = { } for ligand in self : if ligand . category in category_dict : category_dict [ ligand . category ] . append ( ligand ) else : category_dict [ ligand . category ] = [ ligand ] return category_dict
Returns the categories of `Ligands` in `LigandGroup`.