content: """Build a sentiment analysis / polarity model
  
  Sentiment analysis can be casted as a binary text classification problem,
  that is fitting a linear classifier on features extracted from the text
  of the user messages so as to guess wether the opinion of the author is
  positive or negative.
  
  In this examples we will use a movie review dataset.
  
  """
  # Author: Olivier Grisel <olivier.grisel@ensta.org>
  # License: Simplified BSD
  
  import sys
  from sklearn.feature_extraction.text import TfidfVectorizer
  from sklearn.svm import LinearSVC
  from sklearn.pipeline import Pipeline
  from sklearn.grid_search import GridSearchCV
  from sklearn.datasets import load_files
  from sklearn.cross_validation import train_test_split
  from sklearn import metrics
  
  
  if __name__ == "__main__":
      # NOTE: we put the following in a 'if __name__ == "__main__"' protected
      # block to be able to use a multi-core grid search that also works under
      # Windows, see: http://docs.python.org/library/multiprocessing.html#windows
      # The multiprocessing module is used as the backend of joblib.Parallel
      # that is used when n_jobs != 1 in GridSearchCV
  
      # the training data folder must be passed as first argument
      movie_reviews_data_folder = sys.argv[1]
      dataset = load_files(movie_reviews_data_folder, shuffle=False)
      print("n_samples: %d" % len(dataset.data))
  
      # split the dataset in training and test set:
      docs_train, docs_test, y_train, y_test = train_test_split(
          dataset.data, dataset.target, test_size=0.25, random_state=None)
  
      # TASK: Build a vectorizer / classifier pipeline that filters out tokens
      # that are too rare or too frequent
      pipeline = Pipeline([
          ('vect', TfidfVectorizer(min_df=3, max_df=0.95)),
          ('clf', LinearSVC(C=1000)),
      ])
  
      # TASK: Build a grid search to find out whether unigrams or bigrams are
      # more useful.
      # Fit the pipeline on the training set using grid search for the parameters
      parameters = {
          'vect__ngram_range': [(1, 1), (1, 2)],
      }
      grid_search = GridSearchCV(pipeline, parameters, n_jobs=-1)
      grid_search.fit(docs_train, y_train)
  
      # TASK: print the cross-validated scores for the each parameters set
      # explored by the grid search
      print(grid_search.grid_scores_)
  
      # TASK: Predict the outcome on the testing set and store it in a variable
      # named y_predicted
      y_predicted = grid_search.predict(docs_test)
  
      # Print the classification report
      print(metrics.classification_report(y_test, y_predicted,
                                          target_names=dataset.target_names))
  
      # Print and plot the confusion matrix
      cm = metrics.confusion_matrix(y_test, y_predicted)
      print(cm)
  
      # import matplotlib.pyplot as plt
      # plt.matshow(cm)
      # plt.show()
  