title: leave one out in Sklearn
body: <p>I am very new in this field. I am using spyder  to run my code: I am trying to run simple leave one out cross validation code from sklearn: </p>
  
  <pre><code>from sklearn.cross_validation import train_test_split
  from sklearn.cross_validation import LeaveOneOut
  
  X = [1, 2 ,3, 4]
  loo = LeaveOneOut()
  for train, test in loo.split(X):
       print ("%s %s" %(train, test))
  </code></pre>
  
  <p>I am getting following error:</p>
  
  <pre><code>TypeError: __init__() takes exactly 2 arguments (1 given)
  </code></pre>
  
  <p>I understand the reason, but do not know what to pass here.</p>