Event problem on Dynamically created combo box in tablewidget

[chistof]

Hi,

I have a QTableWidget, in which I create dynamically some QComboBox. I simplified the code so things might be missing but the important part is in there, it looks like this :

def testPrint(self, index):
 
    print index
 
 
def itemComboBox(self, array, curIndex):
 
    comboBox = QtGui.QComboBox(self)
    comboBox.addItems(array)
    comboBox.setCurrentIndex(curIndex)
 
    return comboBox
 
 
def createTable(self):
 
    tw = self.ui.tableWidget
 
    version = [ 'v01', 'v02', 'v03' ]
 
    cb = []
    for i range(0,len(version)):
 
        cb.append(self.itemComboBox(version,'v01'))
        tw.setCellWidget(i, 0, cb[i])

def testPrint(self, index):

    print index


def itemComboBox(self, array, curIndex):

    comboBox = QtGui.QComboBox(self)
    comboBox.addItems(array)
    comboBox.setCurrentIndex(curIndex)

    return comboBox


def createTable(self):

    tw = self.ui.tableWidget

    version = [ 'v01', 'v02', 'v03' ]

    cb = []
    for i range(0,len(version)):

        cb.append(self.itemComboBox(version,'v01'))
        tw.setCellWidget(i, 0, cb[i])

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So no problem with that, it creates what I need to see and when I go through each rows I get the values I want. However, I'm trying to run a function when the comboBox value get changed. I first tried that :

def createTable(self):
 
    tw = self.ui.tableWidget
 
    version = [ 'v01', 'v02', 'v03' ]
 
    cb = []
    for i range(0,len(version)):
 
        cb.append(self.itemComboBox(version,'v01'))
        cb[i].currentIndexChanged.connect( lambda: self.testPrint(i) ) ###LINE###
        tw.setCellWidget(i, 0, cb[i])

def createTable(self):

    tw = self.ui.tableWidget

    version = [ 'v01', 'v02', 'v03' ]

    cb = []
    for i range(0,len(version)):

        cb.append(self.itemComboBox(version,'v01'))
        cb[i].currentIndexChanged.connect( lambda: self.testPrint(i) ) ###LINE###
        tw.setCellWidget(i, 0, cb[i])

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But with this, for some reason, each combobox returns the value from the last in the list, seems like I keep overriding the event in the loop but I don't see how since I use a list with index. So as a test I quickly tried something simple outside of the loop after getting rid of the line ###LINE###

for k in range(0,len(version)) :
    cb[k].currentIndexChanged.connect( lambda: self.testPrint(k) )

for k in range(0,len(version)) :
    cb[k].currentIndexChanged.connect( lambda: self.testPrint(k) )

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Which still doesn't work, then because I was really suspicious I tried that instead:

cb[0].currentIndexChanged.connect( lambda: self.testPrint(0) )
cb[1].currentIndexChanged.connect( lambda: self.testPrint(1) )
cb[2].currentIndexChanged.connect( lambda: self.testPrint(2) )

cb[0].currentIndexChanged.connect( lambda: self.testPrint(0) )
cb[1].currentIndexChanged.connect( lambda: self.testPrint(1) )
cb[2].currentIndexChanged.connect( lambda: self.testPrint(2) )

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And that works ! I really don't get why going through a loop would not work the same way.

Anyone can save me on this one ?

Cheers
Chris

[yeye_olive]

This problem is not related to Qt, but to the way Python captures variables in a closure. Your lambda refers to the variable i defined in the enclosing loop, and Python's semantics bind it to the variable's name and scope, not to its value at the time the closure is created. In other words, i is evaluated when the lambda is executed, not when it is constructed, therefore all lambdas see the last value of i.

I found a Stack Overflow discussion with possible solutions:
http://stackoverflow.com/questions/2...ture-in-python

By contrast, C++ lets you choose how variables are captured, just like ordinary function parameters (by value or reference).

[chistof]

Thanks !

Reading this made me understood the issue and I actually sorted it out pretty simply :

def testPrint(self, index):
 
        print index
 
 
    def itemComboBox(self, array, curIndex, ID):
 
        comboBox = QtGui.QComboBox(self)
        comboBox.addItems(array)
        comboBox.setCurrentIndex(curIndex)
        comboBox.currentIndexChanged.connect( lambda: self.testPrint(ID) )
 
        return comboBox
 
 
    def createTable(self):
 
        tw = self.ui.tableWidget
 
        version = [ 'v01', 'v02', 'v03' ]
 
        for i range(0,len(version)):
 
            cb = self.itemComboBox(version,'v01',i)
            tw.setCellWidget(i, 0, cb)

def testPrint(self, index):
     
        print index
     
     
    def itemComboBox(self, array, curIndex, ID):
     
        comboBox = QtGui.QComboBox(self)
        comboBox.addItems(array)
        comboBox.setCurrentIndex(curIndex)
        comboBox.currentIndexChanged.connect( lambda: self.testPrint(ID) )
     
        return comboBox
     
     
    def createTable(self):
     
        tw = self.ui.tableWidget
     
        version = [ 'v01', 'v02', 'v03' ]
     
        for i range(0,len(version)):
     
            cb = self.itemComboBox(version,'v01',i)
            tw.setCellWidget(i, 0, cb)

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By passing the i variable when creating the combo box and creating the event in itemComboBox function itself it sorts out the problem.

Thanks again

Chris