En Fri, 20 Mar 2009 09:28:08 -0300, R. David Murray
<rdmur...@bitdance.com> escribió:
Benjamin Peterson <benja...@python.org> wrote:
Márcio Faustino <m.faustino <at> gmail.com> writes:
>
> Executing the example below doesn't produce the expected behavior, but
> using the commented code does. Is this normal, or is it a problem with
> Python? I've tested it with version 2.6.1 on Windows XP.
Here's the way I find it useful to think about this:
When your lambda is created in your for loop inside your __init__ method,
it acquires a pointer to __init__'s local namespace. (That's how I
understand what "closure" means in this case, though I imagine "closure"
probably means something slightly different in computer-science-ese :)
Well, some people would say that the function "closes over" part of its
environment, but that's the idea.
So, when any of those lambdas is executed, they all have a pointer to
the exact same namespace, that of __init__. And when they are called,
__init__'s namespace is in whatever state it was left in when __init__
ended. In this case, that means that 'option' is pointing to the value
it had at the _end_ of the for loop.
That's a pretty good explanation -- I would just substitute "pointer" by
"reference".
Hope this helps. I find that thinking in terms of namespaces helps
me understand how Python works better than any other mental model
I've come across.
Good to know! The Python execution model *is* based on namespaces - any
other mental model won't be accurate past certain point (although some
people insist...)
--
Gabriel Genellina
--
http://mail.python.org/mailman/listinfo/python-list
