code: def _generate_struct_class_slots(self, data_type):
          
          with self.block('__slots__ =', delim=('[', ']')):
              for field in data_type.fields:
                  field_name = fmt_var(field.name)
                  self.emit("'_%s_value'," % field_name)
                  self.emit("'_%s_present'," % field_name)
          self.emit()
docs: Creates a slots declaration for struct classes.
  
          Slots are an optimization in Python. They reduce the memory footprint
          of instances since attributes cannot be added after declaration.