code: def _get_retention_policy_value(self):
          
  
          if self.RetentionPolicy is None or self.RetentionPolicy.lower() == self.RETAIN.lower():
              return self.RETAIN
          elif self.RetentionPolicy.lower() == self.DELETE.lower():
              return self.DELETE
          elif self.RetentionPolicy.lower() not in self.retention_policy_options:
              raise InvalidResourceException(self.logical_id,
                                             "'{}' must be one of the following options: {}."
                                             .format('RetentionPolicy', [self.RETAIN, self.DELETE]))
docs: Sets the deletion policy on this resource. The default is 'Retain'.
  
          :return: value for the DeletionPolicy attribute.