[PyQt] Signals and class inheritance

[Will Hall]

Hi all,

I've noticed an inconsistency with signal inheritance between PyQt4 and
PySide. The following simple example attempts to redefine stateChanged
on a QComboBox in a derived class. I've condensed the problem into the
following example:

from qtpy import QtCore, QtGui, QtWidgets

class CheckBox(QtWidgets.QCheckBox):

	stateChanged = QtCore.Signal(int)
	def __init__(self, parent=None):
		super(CheckBox, self).__init__(parent)

def findSignals(widget):
	metaObject = widget.metaObject()
	for idx in xrange(metaObject.methodCount()):
		if metaObject.method(idx).methodType() == QtCore.QMetaMethod.Signal:
			yield metaObject.method(idx).signature()

def called(state):
	print 'state changed', state

def main():
	app = QtGui.QApplication(sys.argv)

	checkBox = CheckBox()
	checkBox.stateChanged.connect(called)
	print ('SIGNALS=', list(findSignals(checkBox)))

	checkBox.setCheckState(QtCore.Qt.Checked)

I'm using QtPy abstraction library to comapre Pyt4 against PySide, but
the same behaviour is seen when using direct PyQt4/PySide imports.

$ QT_API=pyside python2 test.py
('SIGNALS=', ['destroyed(QObject*)', 'destroyed()',
'customContextMenuRequested(QPoint)', 'pressed()', 'released()',
'clicked(bool)', 'clicked()', 'toggled(bool)', 'stateChanged(int)'])
state changed 2

$ QT_API=pyqt python2 test.py
('SIGNALS=', ['destroyed(QObject*)', 'destroyed()',
'customContextMenuRequested(QPoint)', 'pressed()', 'released()',
'clicked(bool)', 'clicked()', 'toggled(bool)', 'stateChanged(int)',
'stateChanged(int)'])

Notice that in PyQt4 the stateChanged(int) signal is defined twice but
does not trigger my callback function "called()".

Any insight into this would be gratefully received!

Regards,
Will