title: select k in PCA python skitlearn
body: <p>I am trying to use the skitlearn package for PCA .In the documentation website given here
  <a href="http://scikit-learn.org/stable/modules/generated/sklearn.decomposition.PCA.html" rel="nofollow">http://scikit-learn.org/stable/modules/generated/sklearn.decomposition.PCA.html</a></p>
  
  <p>it is said that if n_components == ‘mle’, then mle is used to find the number of principal components but when I run my code </p>
  
  <pre><code>X_reduced = PCA(n_components=mle).fit_transform(self.X)
  </code></pre>
  
  <p>it gives an error message saying that </p>
  
  <p>global name 'mle' is not defined</p>
  
  <p>how can I specify that mle method has to be used .</p>