              dict(list(attrs.items()) + list(kwargs.items()))
              for attrs in self.validated_data
          ]
  
          self.instance = [
              self.child.create(attrs) for attrs in validated_data
          ]
  
          return self.instance
  
      def __repr__(self):
          return representation.list_repr(self, indent=1)
 
</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 
        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.'
            )
              dict(list(attrs.items()) + list(kwargs.items()))
              for attrs in self.validated_data
          ]
  
        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.'
            )
        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.'
            )
        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.'
            )
  
          return self.instance
  
      def __repr__(self):
          return representation.list_repr(self, indent=1)
keep keep keep keep replace replace replace keep keep keep keep keep
 Split out .create and .update on ListSerializer 
rest_framework/serializers.py