          # Determine the existing instance, if this is an update operation.
          instance = getattr(field.parent, 'instance', None)
  
          # Ensure uniqueness.
          filter_kwargs = {field_name: value}
          queryset = self.queryset.filter(**filter_kwargs)
          if instance:
              queryset = queryset.exclude(pk=instance.pk)
          if queryset.exists():
              raise ValidationError(self.message)
 
</s> remove         instance = getattr(field.parent, 'instance', None)
 </s> add         self.instance = getattr(serializer_field.parent, 'instance', None) </s> remove         if instance:
            queryset = queryset.exclude(pk=instance.pk)
 </s> add         if self.instance is not None:
            queryset = queryset.exclude(pk=self.instance.pk) </s> remove     def __call__(self, value):
        field = self.serializer_field

        # Determine the model field name that the serializer field corresponds to.
        field_name = field.source_attrs[0] if field.source_attrs else field.field_name

 </s> add     def set_context(self, serializer_field):
        # Determine the underlying model field name. This may not be the
        # same as the serializer field name if `source=<>` is set.
        self.field_name = serializer_field.source_attrs[0] </s> remove             (field_name, value[field_name]) for field_name in self.fields
 </s> add             (field_name, attrs[field_name]) for field_name in self.fields
        filter_kwargs = {self.field_name: value}
          # Determine the existing instance, if this is an update operation.
          instance = getattr(field.parent, 'instance', None)
  
          # Ensure uniqueness.
        filter_kwargs = {self.field_name: value}
          queryset = self.queryset.filter(**filter_kwargs)
          if instance:
              queryset = queryset.exclude(pk=instance.pk)
          if queryset.exists():
              raise ValidationError(self.message)
keep keep keep keep replace keep keep keep keep keep
 First pass at unique_for_date, unique_for_month, unique_for_year 
rest_framework/validators.py