title: scikit learn clf.fit / score model accuracy
body: <p>I'm build a model <code>clf</code> say </p>
  
  <pre><code>clf = MultinomialNB()
  clf.fit(x_train, y_train)
  </code></pre>
  
  <p>then I want to see my model accuracy using score</p>
  
  <pre><code>clf.score(x_train, y_train)
  </code></pre>
  
  <p>the result was 0.92</p>
  
  <p>My goal is to test against the test so I use</p>
  
  <pre><code>clf.score(x_test, y_test)
  </code></pre>
  
  <p>This one I got <code>0.77</code> , so I thought it would give me the result same as this code below</p>
  
  <pre><code>clf.fit(X_train, y_train).score(X_test, y_test)
  </code></pre>
  
  <p>This I got <code>0.54</code>. Can someone help me understand why would <code>0.77 &gt; 0.54</code> ? </p>