  
      if slug_field:
          include.append(slug_field)
  
      if lookup_field and lookup_field != 'pk':
          include.append(lookup_field)
 
</s>
        # Pending deprecation
  
      if slug_field:
        # Pending deprecation
          include.append(slug_field)
  
      if lookup_field and lookup_field != 'pk':
          include.append(lookup_field)
keep add keep keep keep keep
 introduce lookup_field and add pendingdeprecationwarnings
rest_framework/mixins.py