[Tkinter-discuss] Re: Storing structured, 'widget-specific-data', then loading it back in la ter

[Fredrik Lundh]

Chris Nethery wrote:

>        self.testButton = Tkinter.Button(self.f, font=(('Verdana'), '7'),
>            text='Test', command=self.getStoredData(self.widget))

to figure out why this doesn't work, consider what the following Python
constructs do:

    getStoredData(widget)

    self.getStoredData(self.widget)

    variable = self.getStoredData(self.widget) # what ends up in variable?

    function(keyword=self.getStoredData(self.widget)) # what's passed to the method?

    Widget(command=self.getStoredData(self.widget)) # what's passed to the constructor?

(hint: the "getStoredData(...)" part does the same thing, and returns the same
thing, in all five cases)


to work around this, you can add a local function:

    def my_callback(self=self):
        self.getStoredData(self.widget)
    self.testButton = Tkinter.Button(..., command=my_callback)

(this creates a callable object, my_callback, that has a reference to the "self"
instance variable.  when the object is called, it will call the right getStoredData
method with the right instance variable)


you can also use a lambda, and in this case, you might not even need the
argument binding (at least not if you're using a recent version of Python):

    ... Button(..., command=lambda: self.getStoredData(self.widget))


(but don't add the workaround until you've figured out why the original code
doesn't work)

</F>