self.drag_position=QtGui.QCursor.pos() # need init it first after creation

def mouseMoveEvent(self, event):
    if (event.buttons() == QtCore.Qt.LeftButton):
        self.move(event.globalPos().x() - self.drag_position.x(),
            event.globalPos().y() - self.drag_position.y())
    event.accept()
def mousePressEvent(self, event):
    if (event.button() == QtCore.Qt.LeftButton):
        self.drag_position = event.globalPos() - self.pos()
    event.accept()