More on passing arguments to tkinter button command

Question

I have a number of test files in a single directory. I'm trying to write a GUI to allow me to select and run one of them.

So, I have a loop that scans the directory and creates buttons:

    for fnm in glob.glob ('Run*.py'):
        tstName = fnm[3:-3]      # Discard fixed part of filename
        btn = Button (self, text=tstName,
                      command=lambda: self.test(tstName))
        btn.grid (row=rowNum, column=0, pady=2)
        rowNum += 1

This creates my GUI correctly, with buttons labelled say, A and B but when I press on the button labelled A it passes B to the test method.

I've looked around and found this question How can I pass arguments to Tkinter button's callback command? but the answer doesn't go on to use the same variable name, with a different value, to configure another widget. (In fact, by tying the variable name to the widget name it almost implies that the technique won't work in this case, as I've found.)

I'm very new to Python, but am quite familiar with creating this kind of GUI using Tcl/TK and I recognise this problem - the value of tstName is being passed when I press the button, but I want it to pass the value the variable had when I created it. I know how I'd fix that in Tcl/Tk - I'd define a command string using [list] at creation time which would capture the value of the variable.

How do I do the same in Python?

Bryan Oakley · Accepted Answer · 2013-10-23 11:23:32Z

7

You need to bind the current value of tstName at the time you define the button. The way you're doing it, the value of tstName will whatever it is at the time you press the button.

To bind the value at the time that you create the button, use the value of tstName as the default value of a keyword parameter to the lambda, like so:

btn = Button(..., command=lambda t=tstName: self.test(t))

answered Oct 23, 2013 at 11:23

Bryan Oakley

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2 Comments

tobias_k Over a year ago

Or functools.partial(self.test, tstName)

nurdglaw Over a year ago

Thanks Bryan - that does the trick. If someone would supply a good link to documentation on lambda I'd appreciate it.

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