code: def labels(self, value):
          
          if value is not None:
              assert type(value) is tuple, "'{0}' attribute: '{1}' type is not 'tuple'!".format("labels", value)
              assert len(value) == 2, "'{0}' attribute: '{1}' length should be '2'!".format("labels", value)
              for index in range(len(value)):
                  assert type(value[index]) is unicode, \
                      "'{0}' attribute element '{1}': '{2}' type is not 'unicode'!".format("labels", index, value)
          self.__labels = value
docs: Setter for **self.__labels** attribute.
  
          :param value: Attribute value.
          :type value: tuple