from PySide.QtGui import *

class PaintTest(QScrollArea):

    def __init__(self, parent=None):
        super(PaintTest, self).__init__(parent)
        self.mainWidget = QWidget()
        self.setWidget(self.mainWidget)
        self.setWidgetResizable(True) # DISABLE THIS WITH ABOVE WIDGET ADDED AND THE CUSTOM PAINT EVENT IS NOT TRIGGERED

    def paintEvent( self, event ):
        print 'painting'
        painter = QPainter()
        painter.begin(self.viewport())
        painter.drawText(self.rect(), 'test')
        painter.end()


if __name__ == '__main__':
    import sys
    app = QApplication([])
    app.setStyle("plastique")
    w = PaintTest()
    w.show()
    sys.exit(app.exec_())