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