django many to many post update method via rest

1class GroupMembershipSerializer(ModelSerializer):
2    class Meta:
3        model = Membership
4        fields = ('person',)
5
6class GroupCreateSerializer(ModelSerializer):
7     memberships = GroupMembershipSerializer(many=True, required=False)
8
9    def create(self, validated_data):
10        person_data = validated_data.pop('memberships')
11        group = Group.objects.create(**validated_data)
12        for person in person_data:
13            d=dict(person)
14            Membership.objects.create(group=group, person=d['person'])
15        return group
16
17    def update(self, instance, validated_data):
18        person_data = validated_data.pop('memberships')
19        for item in validated_data:
20            if Group._meta.get_field(item):
21                setattr(instance, item, validated_data[item])
22        Membership.objects.filter(group=instance).delete()
23        for person in person_data:
24            d=dict(person)
25            Membership.objects.create(group=instance, person=d['person'])
26        instance.save()
27        return instance
28
29    class Meta:
30        model = Group
31
32class GroupCreateModelViewSet(ModelViewSet):
33    serializer_class = GroupCreateSerializer
34    queryset = Group.objects.all()