def bond_features_v1(bond, **kwargs):
    """ Return an integer hash representing the bond type.
    
    flipped : bool
        Only valid for 'v3' version, whether to swap the begin and end atom types

    """
    return str((bond.GetBondType(), bond.GetIsConjugated(), bond.IsInRing(),
        sorted([bond.GetBeginAtom().GetSymbol(), bond.GetEndAtom().
        GetSymbol()])))
