code: def _impute_values(self, features):
          
          if self.verbosity > 1:
              print('Imputing missing values in feature set')
  
          if self._fitted_imputer is None:
              self._fitted_imputer = Imputer(strategy="median")
              self._fitted_imputer.fit(features)
  
          return self._fitted_imputer.transform(features)
docs: Impute missing values in a feature set.
  
          Parameters
          ----------
          features: array-like {n_samples, n_features}
              A feature matrix
  
          Returns
          -------
          array-like {n_samples, n_features}