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

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 testset*.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.

-tim

-- ?!ng

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