title: PySide emit signal causes python to crash
body: <p>I am working through the book "Rapid Gui Programming with Python and Qt" and am having a problem on the signals/slots project.  I have downloaded the authors code to compare against my own, and it all looks the same, however, when I emit a signal from a derived spin box class, python just crashes.  Here is the entire code that I have:</p>
  
  <pre><code>import sys
  from PySide.QtCore import *
  from PySide.QtGui import *
  
  class ZeroSpinBox(QSpinBox):
      zeros = 0
  
      def __init__(self, parent=None):
          super(ZeroSpinBox, self).__init__(parent)
          self.connect(self, SIGNAL("valueChanged(int)"), self.checkzero)
  
      def checkzero(self):
          if self.value() == 0:
              self.zeros += 1
              self.emit(SIGNAL("atzero"), self.zeros)
  
  class Form(QDialog):
      def __init__(self, parent= None):
          super(Form, self).__init__(parent)
  
          dial = QDial()
          dial.setNotchesVisible(True)
          spinbox = ZeroSpinBox()
          spinbox.setRange(0,200)
          dial.setRange(0,200)
  
          layout = QHBoxLayout()
          layout.addWidget(dial)
          layout.addWidget(spinbox)
          self.setLayout(layout)
  
          self.connect(dial, SIGNAL("valueChanged(int)"), spinbox, SLOT("setValue(int)"))
          self.connect(spinbox, SIGNAL("valueChanged(int)"), dial, SLOT("setValue(int)"))
          self.connect(spinbox, SIGNAL("atzero"), self.announce)
  
          self.setWindowTitle("Signals and Slots Part 2")
  
      def announce(self, zeros):
          print "ZeroSpinBox has been at zero %d times" % zeros
  
  
  if __name__ == "__main__":
      app = QApplication(sys.argv)
      form = Form()
      form.show()
      app.exec_()
  </code></pre>
  
  <p>My problem occurs when the spinbox goes down to zero, the checkzero(self) method (of the ZeroSpinBox class) gets called, the self.zeros += 1 line is ok, then on the emit line windows reports that Python.exe has crashed.  The error I get is "python.exe has stopped working" and the console reports "Process finished with exit code -1073741819"</p>
  
  <p>Any idea why this is happening?  This is Python 2.7.2 and PyQT4 w/PySide.</p>