code: def text(self, value):
          
          self._text_buffer = observable(mutable_string(value),
              observer=self._flush)
docs: Updates the seven-segment display with the given value. If there is not
          enough space to show the full text, an ``OverflowException`` is raised.
  
          :param value: The value to render onto the device. Any characters which
              cannot be rendered will be converted into the ``undefined``
              character supplied in the constructor.
          :type value: str