Tkinter.Button(... command) lambda and argument problem

[Paul Rubin]

"Jay" <jaysherby at gmail.com> writes:

> I'm having a problem using lambda to use a command with an argument for
> a button in Tkinter.
> 
>                 buttons = range(5)
> 		for x in xrange(5):

> self.highlight(x))
> 			buttons[x].pack(side=LEFT)
> 
> The buttons are correctly numbered 1 through 5, but no matter which
> button I click on, it sends the number 4 as an argument to the
> highlight function.

x is not bound by the lambda and so the lambda body gets it from the
outside environment at the time the body is executed.  You have to
capture it at the time you create the lambda.  There's an ugly but
idiomatic trick in Python usually used for that:

  buttons[x] = Button(frame, text=str(x+1),   \
        command=lambda x=x: self.highlight(x))

See the "x=x" gives the lambda an arg whose default value is set to 
x at the time the lambda is created, as opposed to when it's called.