code: def set(self, option, value=None):
          
          option = self._container.optionxform(option)
          if option in self.options():
              self.__getitem__(option).value = value
          else:
              self.__setitem__(option, value)
          return self
docs: Set an option for chaining.
  
          Args:
              option (str): option name
              value (str): value, default None