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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 on_mouse_wheel(self, event):
 """Zoom with the mouse wheel."""

        # NOTE: not called on OS X because of touchpad
        if event.modifiers:
            return
        dx = np.sign(event.delta[1]) * self._wheel_coeff
        # Zoom toward the mouse pointer.
        x0, y0 = self._normalize(event.pos)
        self.zoom_delta((dx, dx), (x0, y0))