input: 
  def naive_bayes_classifier(train_data, train_labels):
      """ Construct a naive bayes classifier using python to classify emails as spam or not spam.
      Given the training data (train_data) and corresponding labels (train_labels), 
      this function will train the model and return the trained model.
      >>> naive_bayes_classifier([[1, 2], [2, 3], [3, 4]], [0, 1, 0])
      GaussianNB()
      """
      from sklearn.naive_bayes import GaussianNB
      model = GaussianNB()
      model.fit(train_data, train_labels)
      return model
  
output:     from sklearn.naive_bayes import GaussianNB
      model = GaussianNB()
      model.fit(train_data, train_labels)
      return model