I'd prefer a compromise -- the keys should be strings, but should not be required to be valid identifiers. All Python implementations should support this. Rationale: a type check is cheap, and using strings exclusively makes the use of a faster dict implementation possible. A check for a conforming identifier is relatively expensive and serves no purpose except being pedantic.
--Guido On Thu, Feb 5, 2009 at 12:19 PM, Nick Coghlan <ncogh...@gmail.com> wrote: > Michael Haggerty wrote: >> Is this behavior required somewhere by the Python language spec, or is >> it an error that just doesn't happen to be checked, or is it >> intentionally undefined whether this is allowed? > > Generally speaking, Python namespace dictionaries (be it globals(), > locals(), the __dict__ attribute of an instance or a set of keyword > arguments) aren't required to enforce the use of legal identifiers (in > many cases, the CPython variants don't even enforce the use of strings). > > Enforcing legal identifiers is usually the compiler's job and if you're > using dict syntax to access the contents of a namespace, the compiler > doesn't care. > > That laxness is a CPython implementation detail though - other > implementations are quite free to be stricter with their namespaces > (e.g. I believe Jython namespaces use explicitly string-keyed > dictionaries, so Jython would reject the example below). > > Cheers, > Nick. > > P.S. An example of messing about with a class's dictionary in CPython: > > Python 2.5.2 (r252:60911, Jul 31 2008, 17:28:52) > [GCC 4.2.3 (Ubuntu 4.2.3-2ubuntu7)] on linux2 > Type "help", "copyright", "credits" or "license" for more information. >>>> class C: pass > ... >>>> C.__dict__[5] = "Not an identifier!" >>>> C.5 # obviously not allowed > File "<stdin>", line 1 > C.5 # obviously not allowed > ^ > SyntaxError: invalid syntax >>>> C.__dict__['5'] = "Still not an identifier!" >>>> C.5 # still not allowed > File "<stdin>", line 1 > C.5 # still not allowed > ^ > SyntaxError: invalid syntax >>>> C.__dict__[5] > 'Not an identifier!' >>>> getattr(C, 5) > Traceback (most recent call last): > File "<stdin>", line 1, in <module> > TypeError: getattr(): attribute name must be string >>>> getattr(C, '5') > 'Still not an identifier!' > > Cheers, > Nick. > > -- > Nick Coghlan | ncogh...@gmail.com | Brisbane, Australia > --------------------------------------------------------------- > _______________________________________________ > 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/guido%40python.org > -- --Guido van Rossum (home page: http://www.python.org/~guido/) _______________________________________________ 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
