[Python-Dev] PEP for Better Control of Nested Lexical Scopes (original) (raw)

Thomas Wouters thomas at xs4all.net
Tue Feb 21 15:27:54 CET 2006

On Tue, Feb 21, 2006 at 08:02:08AM -0500, Jeremy Hylton wrote:

The lack of support for rebinding names in enclosing scopes is certainly a wart. I think option one is a better fit for Python, because it more closely matches the existing naming semantics. Namely that assignment in a block creates a new name unless a global statement indicates otherwise. The revised rules would be that assignment creates a new name unless a global or XXX statement indicates otherwise.

I agree with Jeremy on this. I've been thinking about doing something like this myself, but never got 'round to it. It doesn't make working with closures much easier, and I doubt it'll encourage using closures much, but it does remove the wart of needing to use mutable objects to make them read-write.

The names of naming statements are quite hard to get right, I fear. I don't particularly like "use." It's too generic. (I don't particularly like "scope" for option 2, either, for similar reasons. It doesn't indicate what kind of scope issue is being declared.) The most specifc thing I can think of is "free" to indicate that the variable is free in the current scope. It may be too specialized a term to be familiar to most people.

I was contemplating 'enclosed' as a declaration, myself. Maybe, if there's enough of a consent on any name before Python 2.5a1 is released, and the feature isn't going to make it into 2.5, we could ease the introduction of a new keyword by issuing warning about the keyword in 2.5 already. (Rather than a future-import to enable it in 2.6.) Maybe, and only if there's no doubt about how it's going in, of course.

-- Thomas Wouters <thomas at xs4all.net>

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