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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 pos(self):
 """ The position of this event in the local coordinate system of the visual. """

        if self._pos is None:
            tr = self.visual.get_transform('canvas', 'visual')
            self._pos = tr.map(self.mouse_event.pos)
        return self._pos