old_contents: import numpy as np
  
  
  def overwrite_labels(y):
      classes = np.unique(y)
      y[y==classes[0]] = -1
      y[y==classes[1]] = 1
      return y
  
new_contents: import numpy as np
  from sklearn import cross_validation
  
  
  def overwrite_labels(y):
      classes = np.unique(y)
      y[y==classes[0]] = -1
      y[y==classes[1]] = 1
      return y
  
  
  def train_test_split(X, y, test_size=0.2):
      data = cross_validation.train_test_split(X, y, test_size=test_size)
      training = data[0], data[2]
      test = data[1], data[3]
      return training, test
  
subject: Add data splitter for cross validation