How can the function lambda access to my loop or loop using kivy?

Question

I am new to Kivy and Python and i am trying to develop an application that is based on Instagram Layout interface.

First i defined a class ImageButton that will make me create a image button:

class ImageButton(ButtonBehavior, Image):
    pass

Then i used this class to create image button in a grid. here is my Code :

class AllImage(BoxLayout):
    # screen_manager = ObjectProperty()

    def __init__(self, **kwargs):
        BoxLayout.__init__(self, **kwargs)
        self.orientation='vertical'
        self.sizable_from = 'top'
        splitter = Splitter(sizable_from = 'bottom')
        root = ScrollView()

        gridtest = GridLayout(cols=2, spacing=10)

        layout = GridLayout(cols=4, spacing=10)


        self.add_widget(splitter)
        super(AllImage, self).__init__(**kwargs)
        for im in IMAGES_NAMES:
            if IMAGES_NAMES != None :
                btn = ImageButton(source = im+'.png')
                btn.bind(on_press=  lambda a:gridtest.add_widget(ImageButton(source = im+'.png') ))

                layout.add_widget(btn)


        splitter.add_widget(gridtest)
        root.add_widget(layout)

        self.add_widget(root)

My current goal is to add the ImageButton in the grid layoutto the grid gridtest when i press on the imagebutton.

The problem i am encountering now isbtn.bind(on_press= lambda a:gridtest.add_widget(ImageButton(source = im+'.png') )) When i press the ImageButton i don't have the image i pressed in the 2nd grid but the last image in the 1st grid.

I think the problem come from lambda because it don't have the access to my loop and i can't do a loop on it. So what is the solution ?

Answer 1

Closures in Python (which you are creating with the lambda here) are late binding, the value is looked up when the function is invoked (in effect, using the last value for the loop variable if defined in a loop).

The solution is to pass im as a default argument:

lambda a, im=im: # rest same