          Set any attributes on the object that are implicit in the request.
          """
          # pk and/or slug attributes are implicit in the URL.
          pk = self.kwargs.get(self.pk_url_kwarg, None)
          slug = self.kwargs.get(self.slug_url_kwarg, None)
          slug_field = slug and self.slug_field or None
  
          if lookup:
              setattr(obj, self.lookup_field, lookup)
 
</s> remove             exclude = _get_validation_exclusions(obj, pk, slug_field)
 </s> add             exclude = _get_validation_exclusions(obj, pk, slug_field, self.lookup_field) </s> remove def _get_validation_exclusions(obj, pk=None, slug_field=None):
 </s> add def _get_validation_exclusions(obj, pk=None, slug_field=None, lookup_field=None):
        lookup = self.kwargs.get(self.lookup_field, None)
          Set any attributes on the object that are implicit in the request.
          """
          # pk and/or slug attributes are implicit in the URL.
        lookup = self.kwargs.get(self.lookup_field, None)
          pk = self.kwargs.get(self.pk_url_kwarg, None)
          slug = self.kwargs.get(self.slug_url_kwarg, None)
          slug_field = slug and self.slug_field or None
  
          if lookup:
              setattr(obj, self.lookup_field, lookup)
keep keep add keep keep keep keep keep keep
 introduce lookup_field and add pendingdeprecationwarnings 
rest_framework/mixins.py