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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 shift(self, periods=1, freq=None, axis='major'):
 """ Shift index by desired number of periods with an optional time freq. The shifted data will not include the dropped periods and the shifted axis will be smaller than the original. This is different from the behavior of DataFrame.shift() Parameters periods : int Number of periods to move, can be positive or negative freq : DateOffset, timedelta, or time rule string, optional axis : {'items', 'major', 'minor'} or {0, 1, 2} Returns ------- shifted : Panel """

        if freq:
            return self.tshift(periods, freq, axis=axis)

        return super().slice_shift(periods, axis=axis)