code: def cov(self, other=None, pairwise=None, bias=False, **kwargs):
          
          if other is None:
              other = self._selected_obj
              # only default unset
              pairwise = True if pairwise is None else pairwise
          other = self._shallow_copy(other)
  
          def _get_cov(X, Y):
              X = self._shallow_copy(X)
              Y = self._shallow_copy(Y)
              cov = libwindow.ewmcov(X._prep_values(), Y._prep_values(),
                                     self.com, int(self.adjust),
                                     int(self.ignore_na), int(self.min_periods),
                                     int(bias))
              return X._wrap_result(cov)
  
          return _flex_binary_moment(self._selected_obj, other._selected_obj,
                                     _get_cov, pairwise=bool(pairwise))
docs: Exponential weighted sample covariance.