title: PyQt: How to set Combobox Items be Checkable?
body: <p>To keep the GUI widgets number to minimum I need to find a way to give to user a choice of pull-down menu items that could be used to filter out the displayed in a listWidget items. 
  Let's say the listWidget lists 5 different categories of Items: "Cat A", "Cat B","Cat C","Cat D","Cat E". I could implement the radio or checkboxes for each item category. But then 5 radio buttons or checkboxes would take a lot of GUI space. A combobox with the checkable items seems to be a right choice. Any ideas?</p>
  
  <pre><code>from PyQt4 import QtGui, QtCore
  import sys, os
  
  
  class CheckableComboBox(QtGui.QComboBox):
      def __init__(self):    
          super(CheckableComboBox, self).__init__()
  
      def flags(self, index):
          return Qt.ItemIsUserCheckable | Qt.ItemIsSelectable | Qt.ItemIsEnabled
  
  
  class Dialog_01(QtGui.QMainWindow):
      def __init__(self):
          super(QtGui.QMainWindow,self).__init__()
  
          myQWidget = QtGui.QWidget()
          myBoxLayout = QtGui.QVBoxLayout()
          myQWidget.setLayout(myBoxLayout)
          self.setCentralWidget(myQWidget)
  
          self.ComboBox = CheckableComboBox()
          for i in range(3):
              self.ComboBox.addItem("Combobox Item " + str(i))
  
          myBoxLayout.addWidget(self.ComboBox)
  
  
  if __name__ == '__main__':
      app = QtGui.QApplication(sys.argv)
      dialog_1 = Dialog_01()
      dialog_1.show()
      dialog_1.resize(480,320)
      sys.exit(app.exec_())
  </code></pre>