title: PyQt: Get the highlighted index from QComboBox
body: <p>I want to obtain the index of the highlighted item in the QComboBox. How can I access to this variable?</p>
  
  <p>The sample code I have:</p>
  
  <pre><code>    ...
      self.combobox = QtWidgets.QComboBox()
      self.combobox.addItems(['a', 'b', 'c'])
      self.combobox.highlighted.connect(self.return_higlighted_index)
      ...
  
  def return_highlighted_index(self):
      print('The current highlighted index is: ', '?')
  </code></pre>