Why doesn't printer work?

gistfile1.py

from PySide.QtCore import *
from PySide.QtGui import *
from PySide.QtWebKit import *

class Test(QWidget):
  def __init__(self, parent=None):
    super(Test, self).__init__(parent)

    vbox = QVBoxLayout()
    self.setLayout(vbox)

    self.web = QWebView()
    self.web.setHtml("<p style=\"color:red;\">Hello world</p>")

    self.button = QPushButton("Print")
    self.button.clicked.connect(self.doPrint)

    vbox.addWidget(self.web)
    vbox.addWidget(self.button)

  def doPrint(self):
    printer = QPrinter()
    printer.setOutputFormat(QPrinter.PdfFormat)
    printer.setOutputFileName("c:/test.pdf")

    preview = QPrintPreviewDialog(printer)
    preview.paintRequested.connect(self.web.print_)
    preview.exec_()

class MainWindow(QMainWindow):
  def __init__(self, parent=None):
    super(MainWindow, self).__init__(parent)

    test = Test()

    self.setCentralWidget(test)

if __name__ == '__main__':
  import sys
  app = QApplication(sys.argv)
  w = MainWindow()
  w.show()
  sys.exit(app.exec_())