newbie with major "lambda" problem (perhaps a scope problem as well)

[Joe Potter]

On Tue, 26 Jun 2001 17:18:31 GMT, Garry Hodgson <garry at sage.att.com> wrote:

>Joe Potter wrote:
>> 
>> On Tue, 26 Jun 2001 16:09:06 GMT, "Rainer Deyke" <root at rainerdeyke.com> wrote:
>> 
>> >"Joe Potter" <jm7potter at hotmail.com> wrote in message
>> >news:j5ahjtkfmf32lkqtap0q1u6rig385d7b5i at 4ax.com...
>> >>     # the "button" below works like a champ !!
>> >>     #Button(root, text='Fetch',
>> >>                  #command=(lambda v=vars: fetch(v))).pack(side=LEFT)
>> >>
>> >>     # the "button" below does not do anything ??????
>> >>     Button(root, text='Fetch', command=(fetch(vars))).pack(side=LEFT)
>> >
>> >Of course this doesn't work.  It calls 'fetch(vars)', and passes the result
>> >to 'Button'.  Use the lambda, that's what it's there for.  Or use one of the
>> >'curry' alternatives (see archives).
>> 
>> My question is *why* the lambda is allowed to call the perfectly defined function
>> fetch, but a direct call of fetch is not.
>> 
>> In other words --- I already knew that I had to use lambda, but I do not know why!
>
>lambda is a special kind of function.  it creates, on the fly, another,
>un-named
>function, and returns that as its value (much like def, but def also
>binds the
>function to a name).  so the first (commented out) case above
>sets command equal to a function, which will be called when the button
>is clicked.
>in the latter (non-working) case, you actually run your fetch function
>when this code
>is executed, and then bind whatever it returned to the command
>variable.  when you later
>click your button, tkinter tries to use this value as a callback
>funtion, and will fail.
>i'm surprised you don't get an exception.
>
>---

Thanks Garry,

That helped. Along with the other three fellow's words --- I am close to seeing it.

Would you look at my reply to Chris Barker for another little code example along the
same lines?

If I can get that done --- and understood, I'll have it made.

Thanks again, Joe