Question

I’m stuck with the following problem. I’m trying to connect a lambda function to a Signal for passing some extra data eventually.

def createTimeComboBox(self,slotCopy):
    timeComboBox = QComboBox()

    #...

    cmd = lambda func=self.test:func()
    self.connect(timeComboBox, SIGNAL("currentIndexChanged(int)"),cmd)

#...

def test(self, value):
    print value

When I run createTimeComboBox(), I get this error:

TypeError: 'int' object is not callable

Changing

self.connect(timeComboBox, SIGNAL("currentIndexChanged(int)"),cmd)

to

self.connect(timeComboBox, SIGNAL("currentIndexChanged(int)"),self.test)

works fine, but I would like to be able to pass the slotCopy variable as well, so assumed that I need to use the lambda approach.

I had done this previously with a QPushButton‘s clicked() signal and that worked fine.

def createToDoctorButton(self,extraData):
    toDoctorButton = QPushButton()

    cmd = lambda func=self.goToDoctor:func(extraData)
    self.connect(toDoctorButton,  SIGNAL('clicked()'),cmd)

    return toDoctorButton

def goToDoctor(self,extraData):
    print extraData

I hope this makes sense – does anyone have any ideas? Thanks for any suggestions!
Cheers
Dave

Answer 1

Your lambda accepts a parameter (func):

lambda func=self.test:func() 

Although the parameter has a default, it will be replaced if a parameter is passed. Looking at the signal, currentIndexChanged(int), shows that the signal will pass an integer parameter. func will be the integer coming from currentIndexChanged. Later, doing func() will be effectively trying to call an integer object which obviously is not legal (as the error indicates)

You need another parameter in your lambda to “catch” the passed parameter without overriding the func parameter:

cmd = lambda value, func=self.test: func(value)

By the way, your test method expects a parameter, so you can’t just do func().

You didn’t have that problem with the clicked() signal because it doesn’t pass a parameter to replace the default value.