'Provide an iterable for use with write_pack_objects.
:return: Object that can iterate over (object, path) tuples
and provides __len__'

def pack_tuples(self):

    class PackTupleIterable(object, ):
        def __init__(self, pack):
            self.pack = pack
        def __len__(self):
            return len(self.pack)
        def __iter__(self):
            return ((o, None) for o in self.pack.iterobjects())
    return PackTupleIterable(self)
