docs: def get_accuracy(self, scalar=None):
          """Num_True_Positive / Num_Samples"""
          # to get a Series instead of a dict:
          # (np.diag(c).astype(float) / c.T.sum())
          #     == pd.Series(self.sensitivity)
          if ((not self._scalar_stats and not scalar and self._num_classes > 2) or
                  ((scalar is False or self._scalar_stats is False) and self._num_classes > 1)):
              return pd.Series(PrettyDict([(k, safe_div(self[k][k], self._num_total)) for k in self.columns]))
          return self._binary_accuracy