QPainter and QScrollArea plactice

#!/usr/bin/env python
# -*- coding: utf-8 -*-

import sys

from PyQt4 import QtCore,QtGui

class paintArea(QtGui.QWidget):

    def __init__(self):
        super(paintArea, self).__init__()

        self.setMinimumWidth(500)
        self.setMinimumHeight(500)

        self.offscreen = QtGui.QPixmap(1000,1000)

        painter = QtGui.QPainter()
        painter.begin(self.offscreen)
        painter.setPen(QtCore.Qt.yellow)
        for i in range(10):
            painter.drawLine(10,i*10,100,i*10)
        painter.end()

    def paintEvent(self,e):
        painter = QtGui.QPainter()
        painter.begin(self)
        painter.drawPixmap(0,0,self.offscreen)
        painter.end()

class scrollArea(QtGui.QWidget):
    def __init__(self):
        super(scrollArea, self).__init__()

        self.scrollArea = QtGui.QScrollArea(self)

        self.scrollArea.setVerticalScrollBarPolicy( QtCore.Qt.ScrollBarAlwaysOn )
        self.scrollArea.setWidgetResizable(False)

        self.paintArea = paintArea()
        self.scrollArea.setWidget(self.paintArea)

        self.layout = QtGui.QVBoxLayout(self)
        self.layout.addWidget(self.scrollArea)

def main():

    app = QtGui.QApplication(sys.argv)
    ex = scrollArea()
    ex.show()
    sys.exit(app.exec_())

if __name__ == "__main__":
    main()