code: def train(self, *args, **kwargs):
          
          try:
              self.classifier = self.nltk_class.train(self.train_features,
                                                      *args, **kwargs)
              return self.classifier
          except AttributeError:
              raise ValueError("NLTKClassifier must have a nltk_class"
                               " variable that is not None.")
docs: Train the classifier with a labeled feature set and return the
          classifier. Takes the same arguments as the wrapped NLTK class. This
          method is implicitly called when calling ``classify`` or ``accuracy``
          methods and is included only to allow passing in arguments to the
          ``train`` method of the wrapped NLTK class.
  
          .. versionadded:: 0.6.2
  
          :rtype: A classifier