[PyQt] [PyQt5 BUG] the 3rd parameter of QAbstractItemModel::dataChanged() is optional

[iMath]

when I run the code here 
http://codepad.org/ubtleeFG
the following error happened 
>>> 
Traceback (most recent call last):
  File "E:\g.py", line 22, in timerHit
    self.dataChanged.emit (topLeft, topLeft);    
TypeError: QAbstractItemModel.dataChanged[QModelIndex, QModelIndex, list-of-int] signal has 3 argument(s) but 2 provided



the cause is that the 3rd parameter of 
void QAbstractItemModel::dataChanged(const  QModelIndex &  topLeft, const QModelIndex & bottomRight, const  QVector<int> & roles = QVector<int> ())  [signal]
 is optional,while in PyQt5 it seems not .
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