          )
  
      def save(self, **kwargs):
          """
          Save and return a list of object instances.
          """
 
</s> remove         self.instance = [
            self.child.create(attrs) for attrs in validated_data
        ]
 </s> add         if self.instance is not None:
            self.instance = self.update(self.instance, validated_data)
            assert self.instance is not None, (
                '`update()` did not return an object instance.'
            )
        else:
            self.instance = self.create(validated_data)
            assert self.instance is not None, (
                '`create()` did not return an object instance.'
            ) </s> remove         assert self.instance is None, (
            "Serializers do not support multiple update by default, only "
            "multiple create. For updates it is unclear how to deal with "
            "insertions and deletions. If you need to support multiple update, "
            "use a `ListSerializer` class and override `.save()` so you can "
            "specify the behavior exactly."
        )

 </s> add 
    def update(self, instance, validated_data):
        raise NotImplementedError(
            "Serializers with many=True do not support multiple update by "
            "default, only multiple create. For updates it is unclear how to "
            "deal with insertions and deletions. If you need to support "
            "multiple update, use a `ListSerializer` class and override "
            "`.update()` so you can specify the behavior exactly."
        )

    def create(self, validated_data):
        return [
            self.child.create(attrs) for attrs in validated_data
        ]

          )
  
    def update(self, instance, validated_data):
        raise NotImplementedError(
            "Serializers with many=True do not support multiple update by "
            "default, only multiple create. For updates it is unclear how to "
            "deal with insertions and deletions. If you need to support "
            "multiple update, use a `ListSerializer` class and override "
            "`.update()` so you can specify the behavior exactly."
        )

    def create(self, validated_data):
        return [
            self.child.create(attrs) for attrs in validated_data
        ]

      def save(self, **kwargs):
          """
          Save and return a list of object instances.
          """
keep add keep keep keep keep
 Split out .create and .update on ListSerializer 
rest_framework/serializers.py