PyQt/Pyside - Create & Connect Dynamically - capturing function and arguments in lambda [duplicate]

Question

I'm trying to recreate the windows note pad.

I'm currently messing with the QMenuBar

I made a dictionary with all the menus and actions it will have in the following pattern:

menus = {'File':[['New', 'Ctrl+n'],
                 ['Open', 'Ctrl+o'],
                 ['Save', 'Ctrl+s'],
                 ['Save as...', None],
                 'Separator', 
                 # and so on

Then I iterate over that dict, and created the menus and actions successfully and stored them in a second dictionary.

Now I'm trying to connect each action[new, open, save, …] to a instance method of the same name.

I'm doing like so:

for action in menus[m]:
    action = menu.addAction(action[0])

    if action[1]:
        action.setShortcut(QKeySequence(action[1]))

    if isinstance(action, QAction):
        fname = action[0].lower() 
        # and some other string manipulations
        func = getattr(self,fname)
        action.triggered.connect(lambda arg=action: func(arg))

It connects successfully, but if I try to use any of the actions it does nothing.

I had previously connected actions using lambda functions, but this is the first time I'm using getattr() and lambda together.

Don't use __getattribute__: use func = getattr(self, fname). — ekhumoro
– ekhumoro, Commented Dec 8, 2014 at 17:38
Just as arg=action needs to be bound, so does func - since that, too, changes each time through the loop. — Karl Knechtel
– Karl Knechtel, Commented Aug 16, 2022 at 2:26

Dima Tisnek · Accepted Answer · 2014-12-08 10:06:36Z

5

Found my mistake:

Problem was thatfunc was getting overwritten on every iteration over menus.

fixed it by changing:

action.triggered.connect(lambda arg=action:func(arg))

to

action.triggered.connect(lambda f=func,arg=a:f(arg))

The latter works because a reference to func is stored is taken immediately by default argument in lambda.

edited Dec 8, 2014 at 10:06

Dima Tisnek

11.9k4 gold badges73 silver badges129 bronze badges

answered Dec 8, 2014 at 5:12

f.rodrigues

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