[Python-Dev] Explicit Lexical Scoping (pre-PEP?)

Tim Hochberg tim.hochberg at ieee.org
Thu Jul 6 15:38:54 CEST 2006

Ka-Ping Yee wrote:
> On Wed, 5 Jul 2006, Guido van Rossum wrote:
>> On 7/5/06, Phillip J. Eby <pje at telecommunity.com> wrote:
>>> Using the classic nonsense example:
>>>      def counter(num):
>>>          def inc():
>>>              .num += 1
>>>              return .num
>>>          return inc
>> Would this also use ..num to refer to num in an outer scope two
>> levels removed?
> I don't think there's any need for that.  I see '.num' as just another
> way of saying "num, but don't make a new binding".
> I agree with Guido that the best proposals so far are converging on
> the idea that it's more Pythonic to say "don't make a new binding"
> when a variable is used, than to declare "this is the scope for this
> binding" ahead of time.
> Of those there are two kinds:
>     (a) State once (anywhere in a scope, but preferably at the
>         beginning) that a variable is non-local.  This is like
>         the "global" keyword works now, and this category includes:
>           - Change the meaning of 'global'.
>           - Add a new keyword 'outer' or 'nonlocal', etc.
>     (b) Indicate, when mentioning a variable, that the variable
>         is non-local.  This category includes:
>           - Say 'global.x' or 'outer.x' instead of 'x'.
>           - Say '.x' instead of 'x'.
> My favourite so far is to use a new keyword -- i think changing the
> meaning of 'global' would be misleading.  '.x' is probably my next
> favourite, though i share Guido's concern about allowing both 'x'
> and '.x' to refer to the same thing.
> I see that 'outer' is used as an identifier in hmac.py in the
> standard library and also as a variable in test_set*.py.  On the
> other hand 'nonlocal' does not appear anywhere in the standard
> library.  Thus, 'nonlocal' is the best option that i've seen so far;
> it's less likely to break anything and it says exactly what it means.
> I can't think of a more accurate keyword.

'extant' (= already existing) is probably pretty rare in existing code, 
and has pretty close to exactly the correct meaning, but may be too obscure.


> -- ?!ng
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