[Python-Dev] nonlocal keyword in 2.x? (original) (raw)

Fernando Perez fperez.net at gmail.com
Fri Oct 23 08:07:41 CEST 2009

On Thu, 22 Oct 2009 12:32:37 -0300, Fabio Zadrozny wrote:

Just as a note, the nonlocal there is not a requirement...

You can just create a mutable object there and change that object (so, you don't need to actually rebind the object in the outer scope). E.g.: instead of creating a float in the context, create a list with a single float and change the float in the list (maybe the nonlocal would be nicer, but it's certainly still usable)

Yup, that's what I meant by 'some slightly ugly solutions' in this note:

http://mail.scipy.org/pipermail/ipython-dev/2009-September/005529.html

in the thread that spawned those notes. nonlocal allows for this pattern to work without the ugliness of writing code like:

s = [s]

@somedeco def foo(): s[0] += 1

s = s[0]

just to be able to 'change s' inside the foo() scope.

I felt this was both obvious and ugly enough not to warrant too much explicit mention, but I probably should have left it there for the sake of completeness. Thanks for the feedback.

Cheers,

f

ps - the above shouldn't be taken as either pro or con on the idea of nonlocal in 2.x, just a clarification on why I didn't add the mutable container trick to the original notes.

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