input: 
  from sklearn.naive_bayes import MultinomialNB
  
  def classify_string(input_string: str) -> str:
      """ Classify the input string based on a trained machine learning model.
      >>> classify_string("Hello, how are you?")
      'greeting'
      >>> classify_string("What is the weather today?")
      'question'
      """
      # 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[0]
  
output:     # Feature extraction and transformation from string to numeric
      features = [ord(char) for char in input_string]
  
      # Create an instance of the classifier 
      model = MultinomialNB()
  
      # Train the classifier on the data
      data = [[72, 101, 108, 108, 111, 44, 32, 104, 111, 119, 32, 97, 114, 101, 63], [87, 104, 97, 116, 32, 105, 115, 32, 116, 104, 101, 32, 119, 101, 97, 116, 104, 101, 114, 32, 116, 111, 100, 97, 121, 63]]
      target = ['greeting', 'question']
      model.fit(data, target)
  
      # Make a prediction based on the input
      prediction = model.predict([features])
  
      # Return the prediction
      return prediction[0]