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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def text(self, value):
 """ 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 """

        self._text_buffer = observable(mutable_string(value),
            observer=self._flush)