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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 _get_size(self):
 """ Callable that returns the current `Size`, required by Vt100_Output. """

        if self._chan is None:
            return Size(rows=20, columns=79)
        else:
            width, height, pixwidth, pixheight = self._chan.get_terminal_size()
            return Size(rows=height, columns=width)