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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 callback(self, event):
 """ Selects cells on click. """

        self.init_width()

        if len(self.initial) > 0:
            for cell in self.initial:
                self.color_square(cell[0], cell[1], True)
            self.initial = []
        self.begin_drag = event
        self.color_square(event.x, event.y)