code: def OnRemoveCards(self, removedcards):
          
          self.mutex.acquire()
          try:
              parentnode = self.root
              for cardtoremove in removedcards:
                  (childReader, cookie) = self.GetFirstChild(parentnode)
                  found = False
                  while childReader.IsOk() and not found:
                      if self.GetItemText(childReader) == \
                              str(cardtoremove.reader):
                          (childCard, cookie2) = self.GetFirstChild(childReader)
                          self.SetItemText(childCard, 'no card inserted')
                          found = True
                      else:
                          (childReader, cookie) = \
                              self.GetNextChild(parentnode, cookie)
              self.Expand(self.root)
          finally:
              self.mutex.release()
          self.EnsureVisible(self.root)
          self.Repaint()
docs: Called when a card is removed.
          Removes the card from the tree.