code: def shift(self, periods=1, freq=None, axis='major'):
          
          if freq:
              return self.tshift(periods, freq, axis=axis)
  
          return super().slice_shift(periods, axis=axis)
docs: 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