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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 step_amp(self):
 """ Change the amplitude according to the change rate and drift target. Returns: None """

        difference = self.drift_target - self._raw_value
        if abs(difference) < self.change_rate:
            self.value = self.drift_target
        else:
            delta = self.change_rate * numpy.sign(difference)
            self.value = self._raw_value + delta