If you try to use the python standard unix signal handlers with QCoreApplication the handler never gets called. Comment out the creation(and exec_) call, the signal handler gets called as expected.

So, I'm forced to use the unixSignal qt SIGNAL of QCoreApplication but I can't get it to actually trap the SIGHUP.

Qt Code: 
  1. import sys
  2. import time
  3. from PyQt4 import QtCore
  4.  
  5. HUP_EVENT = QtCore.QEvent.User + 1
  6.  
  7.  
  8. class Application(QtCore.QCoreApplication):
  9.     def __init__(self):
  10.         QtCore.QCoreApplication.__init__(self, sys.argv)
  11.  
  12.         self.connect(self, QtCore.SIGNAL('unixSignal(int)'), self.onUnixSignal)
  13.         self.connect(self, QtCore.SIGNAL('sigHUP()'), self.onSIGHUP)
  14.  
  15.  
  16.     def onUnixSignal(self, signum):
  17.         print 'unix signal'
  18.         if signum == signal.SIGHUP:
  19.             self.postEvent(self, QtCore.QEvent(HUP_EVENT))
  20.  
  21.     def event(self, event):
  22.         print 'In event, %s' % event.type()
  23.         if event.type() == 1:
  24.             self.emit(QtCore.SIGNAL("sigHUP()"))
  25.             return True
  26.  
  27.         return False
  28.  
  29.     def onSIGHUP(self):
  30.         print 'in onsighup'
  31.         self.quit()
  32.  
  33.  
  34. if __name__ == '__main__':
  35.     app = Application()
  36.     sys.exit(app.exec_())
  37.     print 'Done'
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Prints

In event, 67
Hangup
Which shows the unix signal was not trapped.

This shows PyQt trashes the python signal module handlers

Qt Code: 
  1. import signal
  2. import sys
  3. import time
  4. from PyQt4 import QtCore
  5.  
  6. HUP_EVENT = QtCore.QEvent.User + 1
  7.  
  8.  
  9. def sighup_handler(signum, frame):
  10.     print 'python signal handler'
  11.     self.postEvent(self, QtCore.QEvent(HUP_EVENT))
  12.  
  13.  
  14.  
  15. class Application(QtCore.QCoreApplication):
  16.     def __init__(self):
  17.         QtCore.QCoreApplication.__init__(self, sys.argv)
  18.  
  19.         self.connect(self, QtCore.SIGNAL('sigHUP()'), self.onSIGHUP)
  20.  
  21.  
  22.     def event(self, event):
  23.         print 'In event, %s' % event.type()
  24.         if event.type() == HUP_EVENT:
  25.             self.emit(QtCore.SIGNAL("sigHUP()"))
  26.             return True
  27.  
  28.         return False
  29.  
  30.     def onSIGHUP(self):
  31.         print 'in onsighup'
  32.         self.quit()
  33.  
  34.  
  35. if __name__ == '__main__':
  36.     app = Application()
  37.  
  38.     signal.signal(signal.SIGHUP, sighup_handler)
  39.  
  40.     sys.exit(app.exec_())
  41.  
  42.     print 'Done'
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Prints

In event, 67
and then nothing.

Comment out the instantiation of the app and...

Qt Code: 
  1. import signal
  2. import sys
  3. import time
  4. from PyQt4 import QtCore
  5.  
  6. HUP_EVENT = QtCore.QEvent.User + 1
  7.  
  8.  
  9. def sighup_handler(signum, frame):
  10.     print 'python signal handler'
  11.     self.postEvent(self, QtCore.QEvent(HUP_EVENT))
  12.  
  13.  
  14.  
  15. class Application(QtCore.QCoreApplication):
  16.     def __init__(self):
  17.         QtCore.QCoreApplication.__init__(self, sys.argv)
  18.  
  19.         self.connect(self, QtCore.SIGNAL('sigHUP()'), self.onSIGHUP)
  20.  
  21.  
  22.     def event(self, event):
  23.         print 'In event, %s' % event.type()
  24.         if event.type() == HUP_EVENT:
  25.             self.emit(QtCore.SIGNAL("sigHUP()"))
  26.             return True
  27.  
  28.         return False
  29.  
  30.     def onSIGHUP(self):
  31.         print 'in onsighup'
  32.         self.quit()
  33.  
  34.  
  35. if __name__ == '__main__':
  36. #    app = Application()
  37.  
  38.     signal.signal(signal.SIGHUP, sighup_handler)
  39.  
  40. #    sys.exit(app.exec_())
  41.     time.sleep(30)
  42.  
  43.     print 'Done'
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python signal handler
Traceback (most recent call last):
File "sharedb/app.py", line 41, in <module>
time.sleep(30)
File "sharedb/app.py", line 11, in sighup_handler
self.postEvent(self, QtCore.QEvent(HUP_EVENT))
NameError: global name 'self' is not defined