[Python-Dev] replacing 'global'

Mon Oct 27 11:12:02 EST 2003

On Mon, Oct 27, 2003 at 07:11:16AM -0800, Guido van Rossum wrote:
>> Hah. Another argument *against* rebinding by :=, and *for* a nonlocal
> declaration. With 'nonlocal n, m' in increment() (or however it's
> spelled :-) the intent is clear.

I dislike := very much. I think it will confuse newbies and thus be
abused. While I dislike the global declaration, I don't feel strongly
about changing or removing it.
The best alternative I've seen that addresses nested scope and the global
declaration. Is to borrow :: from C++:
 foo = DEFAULT_VALUES
 counter = 0
 def reset_foo():
 ::foo = DEFAULT_VALUES
 def inc_counter():
 ::counter += 1
 def outer():
 counter = 5
 def inner():
 ::counter += outer::counter # increment global from outer
 outer::counter += 2 # increment outer counter
The reasons why I like this approach:
 * each variable reference can be explicit when necessary
 * no separate declaration
 * concise, no wording issues like global
 * similarity between global and nested scopes
 (ie, ::foo is global, scope::foo is some outer scope)
 both the global and nested issues are handled at once
 * doesn't prevent augmented assignment
 * it reads well to me and the semantics are pretty clear
 (although that's highly subjective)
Neal