title: Scikit learn (Python 3.5): Do I need to import a library to make this work?
body: <p>I am working through <a href="https://www.amazon.co.uk/Python-Data-Science-Essentials-Second-ebook/dp/B01MAYMIZ3" rel="nofollow noreferrer">Python Data Science Essentials (2nd Edition)</a>.</p>
  <p>The book provides the code below:</p>
  <pre><code>chosen_random_state = 1
  X_train, X_test, y_train, y_test = cross_validation.train_test_split(X, y, test_size=0.30, ran-dom_state=chosen_random_state)
  print (&quot;(X train shape %s, X test shape %s, \ny train shape %s, y test shape %s&quot; \
  % (X_train.shape, X_test.shape, y_train.shape, y_test.shape))
  h1.fit(X_train,y_train)
  print (h1.score(X_test,y_test)) 
  </code></pre>
  <p>When I try to run it, I get the following error:</p>
  <pre><code>--------------------------------------------------------------------------- 
  NameError                                 Traceback (most recent call last) &lt;ipython-input-137-c5136df13468&gt; in &lt;module&gt;()
            1 chosen_random_state = 1
      ----&gt; 2 X_train, X_test, y_train, y_test = cross_validation.train_test_split(X, y, test_size=0.30, random_state=chosen_random_state)
            3 print (&quot;(X train shape %s, X test shape %s, \ny train shape %s, y test shape %s&quot; % (X_train.shape, X_test.shape, y_train.shape, y_test.shape))
            4 h1.fit(X_train,y_train)
            5 print (h1.score(X_test,y_test))
      
      NameError: name 'cross_validation' is not defined
  </code></pre>
  <p>I suspect that I might have to import a library which the book is not mentioning. I have searched the manuals but cannot find this function. IS this a function I need to create or can someone point me to the relevant library?</p>