I had to lookup top-post :-). On 2/21/06, Bengt Richter <[EMAIL PROTECTED]> wrote: > On Tue, 21 Feb 2006 08:02:08 -0500, "Jeremy Hylton" <[EMAIL PROTECTED]> wrote: > >Jeremy > Hey, only Guido is allowed to top-post. He said so ;-)
The Gmail UI makes it really easy to forget where the q > But to the topic, it just occurred to me that any outer scopes could be given > names > (including global namespace, but that would have the name global by default, > so > global.x would essentially mean what globals()['x'] means now, except it would > be a name error if x didn't pre-exist when accessed via > namespace_name.name_in_space notation. > > > namespace g_alias # g_alias.x becomes alternate spelling of global.x > def outer(): > namespace mezzanine > a = 123 > print a # => 123 > print mezzanine.a # => 123 (the name space name is visible and > functional locally) > def inner(): > print mezzanine.a => 123 > mezznine.a =456 > inner() > print a # = 456 > global.x = re-binds global x, name error if not preexisting. > > This would allow creating mezzanine like an attribute view of the slots in > that local namespace, > as well as making namespace itself visible there, so the access to mezzanine > would look like a read access to > an ordinary object named mezzanine that happened to have attribute slots > matching outer's local name space. > > Efficiency might make it desirable not to extend named namespaces with new > names, function locals being > slotted in a fixed space tied into the frame (I think). But there are tricks > I guess. > Anyway, I hadn't seen this idea before. Seems > > Regards, > Bengt Richter > > > > >On 2/20/06, Almann T. Goo <[EMAIL PROTECTED]> wrote: > >> I am considering developing a PEP for enabling a mechanism to assign to > >> free > >> variables in a closure (nested function). My rationale is that with the > >> advent of PEP 227 , Python has proper nested lexical scopes, but can have > >> undesirable behavior (especially with new developers) when a user makes > >> wants to make an assignment to a free variable within a nested function. > >> Furthermore, after seeing numerous kludges to "solve" the problem with a > >> mutable object, like a list, as the free variable do not seem "Pythonic." > >> I > >> have also seen mention that the use of classes can mitigate this, but that > >> seems, IMHO, heavy handed in cases when an elegant solution using a closure > >> would suffice and be more appropriate--especially when Python already has > >> nested lexical scopes. > >> > >> I propose two possible approaches to solve this issue: > >> > >> 1. Adding a keyword such as "use" that would follow similar semantics as > >> "global" does today. A nested scope could declare names with this keyword > >> to enable assignment to such names to change the closest parent's binding. > >> The semantic would be to keep the behavior we experience today but tell the > >> compiler/interpreter that a name declared with the "use" keyword would > >> explicitly use an enclosing scope. I personally like this approach the > >> most > >> since it would seem to be in keeping with the current way the language > >> works > >> and would probably be the most backwards compatible. The semantics for how > >> this interacts with the global scope would also need to be defined (should > >> "use" be equivalent to a global when no name exists all parent scopes, > >> etc.) > >> > >> > >> def incgen( inc = 1 ) : > >> a = 6 > >> def incrementer() : > >> use a > >> #use a, inc <-- list of names okay too > >> a += inc > >> return a > >> return incrementer > >> > >> Of course, this approach suffers from a downside that every nested scope > >> that wanted to assign to a parent scope's name would need to have the "use" > >> keyword for those names--but one could argue that this is in keeping with > >> one of Python's philosophies that "Explicit is better than implicit" (PEP > >> 20). This approach also has to deal with a user declaring a name with " > >> use" that is a named parameter--this would be a semantic error that could > >> be > >> handled like "global " does today with a SyntaxError. > >> > >> 2. Adding a keyword such as "scope" that would behave similarly to > >> JavaScript's " var" keyword. A name could be declared with such a keyword > >> optionally and all nested scopes would use the declaring scope's binding > >> when accessing or assigning to a particular name. This approach has > >> similar > >> benefits to my first approach, but is clearly more top-down than the first > >> approach. Subsequent "scope" declarations would create a new binding at > >> the > >> declaring scope for the declaring and child scopes to use. This could > >> potentially be a gotcha for users expecting the binding semantics in place > >> today. Also the scope keyword would have to be allowed to be used on > >> parameters to allow such parameter names to be used in a similar fashion in > >> a child scope. > >> > >> > >> def incgen( inc = 1 ) : > >> #scope inc <-- allow scope declaration for bound parameters (not a big > >> fan of this) > >> scope a = 6 > >> def incrementer() : > >> a += inc > >> return a > >> return incrementer > >> > >> This approach would be similar to languages like JavaScript that allow for > >> explicit scope binding with the use of "var" or more static languages that > >> allow re-declaring names at lower scopes. I am less in favor of this, > >> because I don't think it feels very "Pythonic". > >> > >> As a point of reference, some languages such as Ruby will only bind a new > >> name to a scope on assignment when an enclosing scope does not have the > >> name > >> bound. I do believe the Python name binding semantics have issues (for > >> which the "global" keyword was born), but I feel that the "fixing" the > >> Python semantic to a more "Ruby-like" one adds as many problems as it > >> solves > >> since the "Ruby-like" one is just as implicit in nature. Not to mention > >> the > >> backwards compatibility impact is probably much larger. > >> > >> I would like the community's opinion if there is enough out there that > >> think > >> this would be a worthwile endevour--or if there is already an initiative > >> that I missed. Please let me know your questions, comments. > >> > >> Best Regards, > >> Almann > >> > >> -- > >> Almann T. Goo > >> [EMAIL PROTECTED] > >> _______________________________________________ > >> Python-Dev mailing list > >> Python-Dev@python.org > >> http://mail.python.org/mailman/listinfo/python-dev > >> Unsubscribe: > >> http://mail.python.org/mailman/options/python-dev/jeremy%40alum.mit.edu > >> > >> > >> > >_______________________________________________ > >Python-Dev mailing list > >Python-Dev@python.org > >http://mail.python.org/mailman/listinfo/python-dev > >Unsubscribe: > >http://mail.python.org/mailman/options/python-dev/python-python-dev%40m.gmane.org > > > > > _______________________________________________ > Python-Dev mailing list > Python-Dev@python.org > http://mail.python.org/mailman/listinfo/python-dev > Unsubscribe: > http://mail.python.org/mailman/options/python-dev/jeremy%40alum.mit.edu > _______________________________________________ Python-Dev mailing list Python-Dev@python.org http://mail.python.org/mailman/listinfo/python-dev Unsubscribe: http://mail.python.org/mailman/options/python-dev/archive%40mail-archive.com
