code: def PluralityLearner(dataset):
      
      most_popular = mode([e[dataset.target] for e in dataset.examples])
      def predict(example):
          "Always return same result: the most popular from the training set."
          return most_popular
      return predict
docs: A very dumb algorithm: always pick the result that was most popular
      in the training data.  Makes a baseline for comparison.