[Tutor] Minesweeper the return

[Alberto Troiano]

Hey Danny

Thanks for the reply

Please let's talk about this more! *grin*
I'm not sure if I'm following you, what I see here is a function inside 
other function and the first function returns its inside function, but how 
does it work?

I don't know Scheme, but I know a little of C#, VB.NET, Pascal, QBasic and 
C++ 6.0

But I would prefer to talk in theory or in general.

Thanks in advanced

Alberto

>From: Danny Yoo <dyoo at hkn.eecs.berkeley.edu>
>To: Alberto Troiano <albertito_g at hotmail.com>
>CC: tutor at python.org
>Subject: Re: [Tutor] Minesweeper the return
>Date: Mon, 18 Jul 2005 16:10:51 -0700 (PDT)
>
>
>
>On Mon, 18 Jul 2005, Alberto Troiano wrote:
>
>
> > I'm trying to create the buttons dinamically (that's not a problem) the
> > problem is wherever I click the hello function returns the last button I
> > created. I know that the problem is in the lambda part and that the 
>variable
> > i (the one I change the value within the for) but I don't how to fix it
>
>
>Hi Alberto,
>
>Ah, this one comes up a bit.  *grin*  Let's look at the code:
>
>######
>for i in range(self.fil):
>     for j in range(self.col):
>         self.buttonmatrix[i][j]=Button(root,width=1,height=0,
>                                        command=lambda: self.hello(i,j))
>######
>
>The issue is that all the dynamically generated functions are using the
>same 'i' and 'j' variables.  The big issue is that, in Python, for-loops
>rebind the iterating variable name to different values, and that's what's
>causing the issue.
>
>
>Instead of using lambda directly, try something like this:
>
>######
>def make_hello(x, y):
>     def new_hello_function():
>         self.hello(x, y)
>     return new_hello_function
>
>for i in range(self.fil):
>     for j in range(self.col):
>         self.buttonmatrix[i][j]=Button(root,width=1,height=0,
>                                        command=make_hello(i, j))
>######
>
>
>There's some subtle lexical-binding stuff going on there, so if you'd
>like, we can talk about this more.  If you're familiar with another
>programming language with lexical scope (like Scheme), we can talk about
>in terms of that language too.
>
>
>Hope this helps!
>
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Gaucho