code: def tracking_error(self, benchmark, ddof=0):
          
  
          er = self.excess_ret(benchmark=benchmark)
          return er.anlzd_stdev(ddof=ddof)
docs: Standard deviation of excess returns.
  
          The standard deviation of the differences between
          a portfolio's returns and its benchmark's returns.
          [Source: CFA Institute]
  
          Also known as: tracking risk; active risk
  
          Parameters
          ----------
          benchmark : {pd.Series, TSeries, 1d np.ndarray}
              The benchmark security to which `self` is compared.
          ddof : int, default 0
              Degrees of freedom, passed to pd.Series.std().
  
          Returns
          -------
          float