      if slug_field:
          # Pending deprecation
          include.append(slug_field)
  
      return [field.name for field in obj._meta.fields if field.name not in include]
  
  
  class CreateModelMixin(object):
      """
 
</s> remove             exclude = _get_validation_exclusions(obj, pk, slug_field)
 </s> add             exclude = _get_validation_exclusions(obj, pk, slug_field, self.lookup_field)
    if lookup_field and lookup_field != 'pk':
        include.append(lookup_field)

      if slug_field:
          # Pending deprecation
          include.append(slug_field)
  
    if lookup_field and lookup_field != 'pk':
        include.append(lookup_field)

      return [field.name for field in obj._meta.fields if field.name not in include]
  
  
  class CreateModelMixin(object):
      """
keep keep keep add keep keep keep keep keep
 introduce lookup_field and add pendingdeprecationwarnings 
rest_framework/mixins.py