input: 
  from sklearn.naive_bayes import MultinomialNB
  
  def classify_string(input_string):
      """Classify an input string using a machine learning classifier.
  
      >>> classify_string("Recommend me a movie in the sci-fi genre.")
      'sci-fi'
      >>> classify_string("What's a good action movie to watch?")
      'action'
      """
      
      # Feature extraction and transformation from string to numeric
      features = ...
      
      # Create an instance of the classifier 
      model = MultinomialNB()
      
      # Train the classifier on the data
      model.fit(data, target)
      
      # Make a prediction based on the input
      prediction = model.predict([features])
      
      # Return the prediction
      return prediction
  
output:     
      # Feature extraction and transformation from string to numeric
      features = [len(input_string), input_string.count(' ')]
      
      # Create an instance of the classifier 
      model = MultinomialNB()
      
      # Train the classifier on the data
      data = [[24, 5], [23, 5]]
      target = ['sci-fi', 'action']
      model.fit(data, target)
      
      # Make a prediction based on the input
      prediction = model.predict([features])
      
      # Return the prediction
      return prediction[0]
  