          self.format = kwargs.pop('format', None)
  
          # These are pending deprecation
          self.pk_url_kwarg = kwargs.pop('pk_url_kwarg', self.pk_url_kwarg)
          self.slug_field = kwargs.pop('slug_field', self.slug_field)
          default_slug_kwarg = self.slug_url_kwarg or self.slug_field
          self.slug_url_kwarg = kwargs.pop('slug_url_kwarg', default_slug_kwarg)
  
 
</s> remove             exclude = _get_validation_exclusions(obj, pk, slug_field)
 </s> add             exclude = _get_validation_exclusions(obj, pk, slug_field, self.lookup_field)
        if 'pk_url_kwarg' in kwargs:
            msg = 'pk_url_kwarg is pending deprecation. Use lookup_field instead.'
            warnings.warn(msg, PendingDeprecationWarning, stacklevel=2)
        if 'slug_url_kwarg' in kwargs:
            msg = 'slug_url_kwarg is pending deprecation. Use lookup_field instead.'
            warnings.warn(msg, PendingDeprecationWarning, stacklevel=2)
        if 'slug_field' in kwargs:
            msg = 'slug_field is pending deprecation. Use lookup_field instead.'
            warnings.warn(msg, PendingDeprecationWarning, stacklevel=2)

          self.format = kwargs.pop('format', None)
  
          # These are pending deprecation
        if 'pk_url_kwarg' in kwargs:
            msg = 'pk_url_kwarg is pending deprecation. Use lookup_field instead.'
            warnings.warn(msg, PendingDeprecationWarning, stacklevel=2)
        if 'slug_url_kwarg' in kwargs:
            msg = 'slug_url_kwarg is pending deprecation. Use lookup_field instead.'
            warnings.warn(msg, PendingDeprecationWarning, stacklevel=2)
        if 'slug_field' in kwargs:
            msg = 'slug_field is pending deprecation. Use lookup_field instead.'
            warnings.warn(msg, PendingDeprecationWarning, stacklevel=2)

          self.pk_url_kwarg = kwargs.pop('pk_url_kwarg', self.pk_url_kwarg)
          self.slug_field = kwargs.pop('slug_field', self.slug_field)
          default_slug_kwarg = self.slug_url_kwarg or self.slug_field
          self.slug_url_kwarg = kwargs.pop('slug_url_kwarg', default_slug_kwarg)
  
keep keep add keep keep keep keep keep
 introduce lookup_field and add pendingdeprecationwarnings 
rest_framework/relations.py