code: def std(self, ddof=1, *args, **kwargs):
          
  
          # TODO: implement at Cython level?
          nv.validate_groupby_func('std', args, kwargs)
          return np.sqrt(self.var(ddof=ddof, **kwargs))
docs: Compute standard deviation of groups, excluding missing values.
  
          For multiple groupings, the result index will be a MultiIndex.
  
          Parameters
          ----------
          ddof : integer, default 1
              degrees of freedom