title: scikit-learn .predict() default threshold
body: <p>I'm working on a classification problem with unbalanced classes (5% 1's). I want to predict the class, not the probability.</p>
  
  <p>In a binary classification problem, is scikit's <code>classifier.predict()</code> using <code>0.5</code> by default?
  If it doesn't, what's the default method? If it does, how do I change it?</p>
  
  <p>In scikit some classifiers have the <code>class_weight='auto'</code> option, but not all do. With <code>class_weight='auto'</code>, would <code>.predict()</code> use the actual population proportion as a threshold?</p>
  
  <p>What would be the way to do this in a classifier like <code>MultinomialNB</code> that doesn't support <code>class_weight</code>? Other than using <code>predict_proba()</code> and then calculation the classes myself.</p>