PSEP 100 says that the PySide and PyQt signal/slot mechanisms should be
functionally compatible, but I think I found a small functionality difference
(I wasn't able to find the PyQt 4.5 doc, but I'm pretty sure this is just a bug
and not a functionality change in PyQt).  If I try to disconnect a specific
signal/slot before it has been connected, then I get a terminal message saying 

Object::disconnect: No such slot Test::sl(int)

The PyQt docs say that an exception will be raised if the slot is not connected
to the signal or if the signal has no connections at all, so I think this
message needs to be caught and an exception raised instead.  The difference in
functionality doesn't really matter to me, since I would just catch the
exception and pass, but hiding that message would be preferable.

Here's a simple class and script that shows this disconnect message.



from PySide.QtCore import Qt, QObject, Signal

class Test(QObject):
    sig = Signal((int,))

    def __init__(self):
        QObject.__init__(self)
    def con(self):
        self.sig.connect(self.sl)
    def dis(self):
        self.sig[int].disconnect(self.sl)
    def sl(self, i):
        print i
    def call(self):
        self.sig[int].emit(123)

t = Test()
t.dis()
t.con()
t.call()
t.dis()