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

Evan Simpson evan at 4-am.com
Fri Jul 7 18:56:01 CEST 2006

Kevin Jacobs <jacobs at bioinformed.com> wrote:

Why not extend the interface to the locals builtin and add a getitem that returns a proxy to access locals defined in other lexical scopes _via {get/set/del}attr:

def counter(num): num = 1 def inc(): locals[1].num += 1 return outer.num return inc Where, for CPython, locals[n] gives access to NamespaceProxy(sys.getframe(n).flocals).

Two nits: First, I suspect that you meant to write "return locals[1].num". Second, sys._getframe doesn't do what you want, here. It reaches back up the call chain, not out into lexically containing scopes.

That said, I like the idea of giving "locals[]" the meaning you intended. It has the advantage of not adding any new keywords or syntactic constructs, but the disadvantage of not explicitly signaling that locals in a given scope will be twiddled elsewhere. Also, for efficiency's sake, it might be desirable to only allow a literal integer as the index, and to deal with use of "locals[]" at compile time rather than dynamically. I'm not sure how much overhead would be involved in enabling dynamic lookup of arbitrary lexically containing scopes, but I would not want to enable stuff like "locals[i * 2 - 1]".

Cheers,

Evan @ 4-am

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