problem with QtSignals "object has no attribute 'emit'"

[Phil Thompson]

On Sun, 14 Feb 2010 13:17:40 +0100, News123 <news123 at free.fr> wrote:
> Hi,
> 
> I'm having a rather small code snippet, where I create pyQT signals.
> I manage creating a signal as class attribute,
> but I can't create a list of signals or a signal
> as object.member.
> 
> 
>> from PyQt4.QtGui import *
>> from PyQt4.QtCore import *
>> 
>> class MyWin(QMainWindow):
>>     clssig     = pyqtSignal()
>>     sigarr   = [ pyqtSignal() ]
>>     def emit_them(self):
>>         self.objsig = pyqtSignal()
>>         self.clssig.emit()    # works
>>         self.sigarr[0].emit()  # fails 
>>         self.objsig.emit()  # fails
>> 
>> if __name__ == "__main__":
>>     app = QApplication(sys.argv)
>>     win = MyWin()
>>     win.show()
>>     win.emit_them()
>>     sys.exit(app.exec_())
> 
> The two lines marked with fails will fail with following error:
>> AttributeError: 'PyQt4.QtCore.pyqtSignal' object has no attribute 'emit'
> 
> The QT documentation states:
> "New signals should only be defined in sub-classes of QObject."
> 
> I guess, that his is the reason. though I don't know enough about PyQT
> to understand the magic behind.
> 
> 
> Now my question:
> 
> How could I create an array of signals if I wished to?
> 
> I can work aroud it, but would be curious.
> 
> 
> Thanks for shadng some light on this (for me surprising) issue.

You can't create an array of signals.

Signals are defined to both Python and C++. This is done when the class is
defined by introspecting the class attributes - but it doesn't look for
signals any deeper than that, i.e. it won't look into your sigarr list.

Even if it did, there is a second issue. Signals have unbound and bound
versions (much like unbound and bound methods). The class attribute is an
unbound signal that is a descriptor that will return the bound signal. It
is the bound signal that implements the emit() method. It would be possible
for an unbound signal's __call__ method to also return a bound signal so
that you could do something like...

    self.sigarr[0](self).emit()

...but I can't think of a valid use case.

Phil