On 12/09/2014 02:15 AM, memilanuk wrote:
On 12/08/2014 09:30 PM, Ben Finney wrote:
memilanuk <memila...@gmail.com> writes:
...
lambda: update_label2('A', 100)
would this work the same?
(I don't know what you mean here by “the same”; the same as what?)
The above creates a new function, which expects no parameters (because
there are no parameters before its ‘:’).
The function, when called, will return the value of the expression
‘update_label2('A', 100)’.
It looks as though it'd be passing the same two parameters to the same
function...
Yes, it looks that way, and that's what it does. The parameters are
fixed in the expression and will be the same each time the new function
is called.
lambda: 'A', 100: update_label2()
This is a syntax error.
Have you tried experimenting with these? Carefully read the reference
material on the ‘lambda’ syntax, and create some functions and
experiment with them.
Fair enough. What I was trying to do when I got into all this was
something like this:
import tkinter as tk
root = tk.Tk()
root.wm_title('Radio Buttons')
label1 = tk.Label(root)
label1.config(text='Please select an option below.')
label1.pack()
def update_label2(option, value):
selection = "current selection is: \n\n" + str(option) + ": " +
str(value)
label2.config(text=selection)
var = tk.IntVar()
var.set(100)
R1 = tk.Radiobutton(root, text='A', value=100, variable=var,
command=lambda: update_label2('A', 100))
R1.pack(anchor='center')
R2 = tk.Radiobutton(root, text='B', value=80, variable=var,
command=lambda option='B', value=80: update_label2())
R2.pack(anchor='center')
R3 = tk.Radiobutton(root, text='C', value=60, variable=var,
command=lambda: update_label2('C', 60))
R3.pack(anchor='center')
label2 = tk.Label(root)
label2.config(text='Current selection is: \n \nA: 100')
label2.pack()
root.mainloop()
So to me, the purpose of 'lambda' in this case is to call a function
when a particular widget - in this case a radio button - is clicked.
Thats why I wondered if 'lambda: update_label2('A', 100)' - where I'm
using lambda to call another function, with the parameters inside the
parentheses, was equivalent to 'lambda 'A', 100: update_label2()' where
I would be using lambda to 'feed' the parameters to the function.
You can certainly use lambda to "feed" the values, but you're calling
the update_label function with no arguments. If you always want to pass
those particular values, stick to the
command=lambda: update_label2('A', 100))
version. If the values have to be calculated, then you might want
command=lambda: update_label2('A', 100*SOME_GLOBAL))
But specifying arguments to the lambda that you don't use makes no sense.
command=lambda option='B', value=80: update_label2())
The locals option and value aren't being used, so they're just wasted
characters. In another context, something like:
command=lambda option='B', value=80: update_label2(option, 2*value))
might make sense, but since tkinter isn't going to pass any arguments to
the function, there's no point in declaring them.
Try writing ordinary functions for your command= to use, and experiment
with those.
def mycallback():
update_label2('A', 100)
command = mycallback
Notice that tkinter will not be passing any arguments, so there's no
point in having any parameters in mycallback(). But also notice that if
you do declare such parameters (with default values), those values won't
be automatically passed to the update_label() function.
In other words, this:
def mycallback(a = 5, b = 12):
update_label2()
doesn't automagically pass a and b into update_label2.
--
DaveA
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