[PyQt] Possible bug with new signal-slot connection

[Alexander Bruy]

Hi all,

I try to use new style for signal-slot connection [0] in my project. And
have one problem that looks like bug in PyQt.

There is a dialog window with QDialogButtonBox, which has two buttons
OK and Close. During the program execution I need to change behavior
of Close button: pressing this button should not close the dialog but invoke
another slot. Using old signal-slot connection I implement this as

self.btnClose = self.buttonBox.button( QDialogButtonBox.Close )
# disconnect from rejected() slot
QObject.disconnect( self.buttonBox, SIGNAL( "rejected()" ), self.reject )
# and connect to user-defined slot
QObject.connect( self.btnClose, SIGNAL( "clicked()" ), self.stopProcessing )
....
# restore original state
QObject.disconnect( self.btnClose, SIGNAL( "clicked()" ), self.stopProcessing )
QObject.connect( self.buttonBox, SIGNAL( "rejected()" ), self.reject )

And all works fine as I want. But when i use new style for signal-slot
connection
in same code

self.btnClose = self.buttonBox.button( QDialogButtonBox.Close )
self.buttonBox.rejected.disconnect( self.reject )
self.btnClose.clicked.connect( self.stopProcessing )
...
self.btnClose.clicked.disconnect( self.stopProcessing )
self.buttonBox.rejected.connect( self.reject )

I get error in run-time

line 147, in prepareProcess
self.buttonBox.rejected.disconnect( self.reject )
TypeError: disconnect() failed between ‘rejected’ and ‘reject’

Dialog designed in QtDesigner and compiled to Python code using
pyuic4.

After some investigating I found that pyuic4 generates code using
old-style signal-slot connections

QtCore.QObject.connect(self.buttonBox,
QtCore.SIGNAL(_fromUtf8("accepted()")), Dialog.accept)
QtCore.QObject.connect(self.buttonBox,
QtCore.SIGNAL(_fromUtf8("rejected()")), Dialog.reject)

If I replace this string in generated file with new style connections

self.buttonBox.accepted.connect(Dialog.accept)
self.buttonBox.rejected.connect(Dialog.reject)

my code again works fine. This was tested under Linux: with
Python 2.6.6, Qt 4.7.0 and PyQt 4.8.1. And under Windows using
 - Python 2.7.3, PyQt 4.9, Qt 4.8.0
 - Python 3.2.2, PyQt 4.9.1, Qt 4.8.0.

I think that incompatibility between new and old style for signal-slot
connections is a major bug that can cause many problems when UI
created in Designer and some signals and slots should be connected
and disconnected in run-time.

I create simple demo for this bug, find it attached.

[0] http://www.riverbankcomputing.co.uk/static/Docs/PyQt4/html/new_style_signals_slots.html

Thanks and sorry for my English

-- 
Alexander Bruy
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