code: def diff(self, periods=1):
          
          result = algorithms.diff(com.values_from_object(self), periods)
          return self._constructor(result, index=self.index).__finalize__(self)
docs: First discrete difference of element.
  
          Calculates the difference of a Series element compared with another
          element in the Series (default is element in previous row).
  
          Parameters
          ----------
          periods : int, default 1
              Periods to shift for calculating difference, accepts negative
              values.
  
          Returns
          -------
          Series
              First differences of the Series.
  
          See Also
          --------
          Series.pct_change: Percent change over given number of periods.
          Series.shift: Shift index by desired number of periods with an
              optional time freq.
          DataFrame.diff: First discrete difference of object.
  
          Examples
          --------
          Difference with previous row
  
          >>> s = pd.Series([1, 1, 2, 3, 5, 8])
          >>> s.diff()
          0    NaN
          1    0.0
          2    1.0
          3    1.0
          4    2.0
          5    3.0
          dtype: float64
  
          Difference with 3rd previous row
  
          >>> s.diff(periods=3)
          0    NaN
          1    NaN
          2    NaN
          3    2.0
          4    4.0
          5    6.0
          dtype: float64
  
          Difference with following row
  
          >>> s.diff(periods=-1)
          0    0.0
          1   -1.0
          2   -1.0
          3   -2.0
          4   -3.0
          5    NaN
          dtype: float64