title: Error when I pass a different form of K in knearest neighbours(Sci kit learn)
body: <p>When running k nearest neighbors in scikit learn, When I set k as 21 I get value error. but when I set k as <code>k=np.arange(20) +1</code> I dont get an error, so what is the difference between these two? </p>
  
  <pre><code>k = np.arange(21)
  
  parameters = {'n_neighbors': k}
  knn = sklearn.neighbors.KNeighborsClassifier()
  
  clf = sklearn.grid_search.GridSearchCV(knn, parameters, cv=10)
  clf.fit(X_train, Y_train)
  
  ValueError: Invalid shape in axis 1: 0.
  </code></pre>
  
  <p>Also can some one explain me what is the </p>
  
  <pre><code>a = clf.grid_scores_
  scores = [b.cv_validation_scores for b in a]
  </code></pre>
  
  <p>Out put of scores is as follows :</p>
  
  <pre><code>array([ 1.        ,  0.90909091,  1.        ,  0.72727273,  0.9       ,
           1.        ,  1.        ,  1.        ,  1.        ,  0.88888889]),
  </code></pre>
  
  <p><code>clf.grid_scores_</code> is accuracy of the classifier but what is that <code>cv_validation</code> scores?? </p>