title: Assign a function to a change in QcomboBox
body: <p>I have tried to call a function when there has been a change in the QcomboBox. When the comboBox is changed it will update the xAxis on a graph. Is there a way to call a function when a different item is selected from the comboBox? </p>
  
  <pre><code>def updateGraph():
      print("update graph")
  
  proxy = QtGui.QGraphicsProxyWidget()
  xAxis = QtGui.QComboBox()
  proxy.setWidget(xAxis)
  xAxis.currentIndexChanged().connect(updateGraph)
  </code></pre>
  
  <p>Error that is currently produced:</p>
  
  <pre><code>TypeError: native Qt signal is not callable
  </code></pre>