title: Unresolved reference "sklearn" in Python while importing GaussianNB
body: <p>I am trying to execute the following statements in PyCharm on Windows. I get the error message in the 4th line importing GaussianNB - sklearn: Unresolved Reference. Is there any package needed to be included or some other way to resolve this?</p>
  
  <pre><code>import numpy as np
  X = np.array([[-1, -1], [-2, -1], [-3, -2], [1, 1], [2, 1], [3, 2]])
  Y = np.array([1, 1, 1, 2, 2, 2])
  from sklearn.naive_bayes import GaussianNB
  clf = GaussianNB()
  clf.fit(X, Y)
  print(clf.predict([[-0.8, -1]]))
  </code></pre>