[Python-Dev] "as" keyword woes

Virgil Dupras hsoft at hardcoded.net
Sun Dec 7 00:01:39 CET 2008

On 06 Dec 2008, at 20:38, Warren DeLano wrote:

>> Date: Fri, 05 Dec 2008 22:22:38 -0800
>> From: Dennis Lee Bieber <wlfraed at ix.netcom.com>
>> Subject: Re: "as" keyword woes
>> To: python-list at python.org
>> Message-ID: <bqadnTS6jM21h6fUnZ2dnUVZ_uydnZ2d at earthlink.com>
>> 	I'm still in the dark as to what type of data could
>> even inspire the
>> use of "as" as an object name... A collection of "a" objects? In  
>> which
>> case, what are the "a"s? <G>
> Please let me clarify.  It is not "as" as a standalone object that we
> specifically miss in 2.6/3, but rather, the ability to use ".as"  
> used as
> a method or attribute name.
> In other words we have lost the ability to refer to "as" as the
> generalized OOP-compliant/syntax-independent method name for casting:
> new_object = old_object.as(class_hint)
> # For example:
> float_obj = int_obj.as("float")
> # or
> float_obj = int_obj.as(float_class)
> # as opposed to something like
> float_obj = int_obj.asFloat()
> # which requires a separate method for each cast, or
> float_obj = (float)int_obj
> # which required syntax-dependent casting [language-based rather than
> object-based].
> Of course, use of explicit casting syntax "(float)" is fine if you're
> restricting yourself to Python and other languages which support
> casting, but that solution is unavailable inside of a pure OOP
> message-passing paradigm where object.method(argument) invocations are
> all you have to work with.
> Please note that use of object.asClassname(...) is a ubiqitous
> convention for casting objects to specific classes (seen in  
> ObjectiveC,
> Java, SmallTalk, etc.).
> There, I assert that 'object.as(class_reference)' is the simplest and
> most elegant generalization of this widely-used convention.  Indeed,  
> it
> is the only obvious concise answer, if you are limited to using  
> methods
> for casting.
> Although there are other valid domain-specific uses for "as" as  
> either a
> local variable or attribute names (e.g. systematic naming: as, bs,  
> cs),
> those aren't nearly as important compared to "as" being available as  
> the
> name of a generalized casting method -- one that is now strictly  
> denied
> to users of Python 2.6 and 3.
> As someone somewhat knowledgable of how parsers work, I do not
> understand why a method/attribute name "object_name.as(...)" must
> necessarily conflict with a standalone keyword " as ".  It seems to me
> that it should be possible to unambiguously separate the two without
> ambiguity or undue complication of the parser.
> So, assuming I now wish to propose a corrective PEP to remedy this
> situation for Python 3.1 and beyond, what is the best way to get  
> started
> on such a proposal?
> Cheers,
> Warren

As long as "as" is widely known as a keyword, I don't see the problem.  
Every python developer knows that the convention is to add a trailing  
underscore when you want to use a reserved word in your code. Besides,  
your examples are quite abstract. I'm sure it's possible to find good  
examples for "while", "with", "import", "from" (I often use "from_")  
or "try" as well. Or perhaps that the python keywords should be "as_"  
so we leave "as" free for eventual methods?

As for the implicit proposition of allowing keywords only for methods,  
I agree with Guido about it being a slippery slope. So we would end up  
with a language where it is allowed to name methods after keywords,  
but not functions (they can be declared in the local scope)? Yikes! Oh  
well, maybe it's possible for an intelligent parser to distinguish  
between keywords and function references, but think of the poor  
grammar highlighters in all source editors! What a nightmare it will  
be for them. Anyway, is there any language that does this, allowing  
keywords as method names? I don't know, but if not, there's probably a  
reason for it.

Your views on code elegance are also rather Javaish. I'd go for  
"class_reference(object)" (and why the heck would you "be limited to  
using method for casting"?).


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