Lord Eldritch wrote:
Hi
Maybe this is maybe something it has been answered somewhere but I haven't
been able to make it work. I wanna pass one variable to a callback function
and I've read the proper way is:
Button(......, command=lambda: function(x))
So with
def function(a): print a
I get the value of x. Ok. My problem now is that I generate the widgets in a
loop and I use the variable to 'label' the widget:
for x in range(0,3): Button(......, command=lambda: function(x))
so pressing each button should give me 0,1,2.
But with the lambda, I always get the last index, because it gets actualized
at each loop cycle. Is there any way to get that?
A lambda expression is just an unnamed function. At the point the
function is /called/ 'x' is bound to 3, so that's why 'function' is
always called with 3.
A function's default arguments are evaluated when the function is
/defined/, so you can save the current value of 'x' creating the
function (the lambda expression, in this case) with a default argument:
for x in range(0,3):
Button(......, command=lambda arg=x: function(arg))
The following will also work, although you might find the "x=x" a bit
surprising/confusing if you're not used to how Python works:
for x in range(0,3):
Button(......, command=lambda x=x: function(x))
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