Re: [Tutor] Why does this function execute before being called?

[Chris Roy-Smith]

On 07/11/15 20:18, Alan Gauld wrote:
On 07/11/15 04:34, Chris Roy-Smith wrote:
def genF(ofield): ...
     for x in range(10):

def second():
     main=Toplevel(root)
     ofield=Text(main, height=15, width=15)
     ofield.pack()
     B3=Button(main, text='exit', command=main.destroy)
     B3.pack()
     B4=Button(main, text='fill text', command=genF(ofield))

You call a function by sup[plying the parens after its name.
So the function gets called here. The normal way to circumvent
that in Tkinter is to use a lambda expression to defer execution,
like so:

B4=Button(main, text='fill text', command=lambda wgt=ofield : genF(wgt))

This certainly wasn't obvious from what I could find on the internet. 
Now I see an application for Lambda

     B4.pack()
     main.mainloop()

I'm not sure you need the second mainloop. I think the
root level mainloop will work for your window too.


Just tried out leaving this second mainloop, and every works the same. I 
had assumed I needed to create a loop the same as the top window.

Thanks for clearing up this mystery

_______________________________________________
Tutor maillist  -  Tutor@python.org
To unsubscribe or change subscription options:
https://mail.python.org/mailman/listinfo/tutor