[Python-3000] pep 3124 plans (original) (raw)

Joe Smith unknown_kev_cat at hotmail.com
Sat Jul 21 19:07:12 CEST 2007

"Guido van Rossum" <guido at python.org> wrote in message news:ca471dc20707210816r4d663cdaqcef7e9f28c150a75 at mail.gmail.com...

On 7/21/07, Joe Smith <unknownkevcat at hotmail.com> wrote:

One of the nice features of Eby's proposal is that more complicated dispatching systems can be added. Perhaps some application needs a dispatching engine that can dispatch based on the value of an objects member. Perhaps the user wants an overload specificly for any product object whose price property equals 0. With Eby's system adding a dispatch engine that supports that is not difficult. This is true. However it comes at a cost. Whenever I see an API that takes a string which is then parsed by the called function as a Python expression (perhaps constrained to a subset of Python) I cringe, especially if the common use is to pass a literal. There are just so many issues with that... It's not colorized by the editor, it's not syntax-checked by either the editor or the Python parser, it requires one to build yet another parser... This is why I don't like the ...when("isinstance(obj, list)") syntax from (I think) RuleDispatch, and I'm glad it's not in the PEP. I'm unclear however on how you would do this otherwise -- is overloading implies() the best approach?

First of all, If i understrand the PEP correectly. that should be: when(funcname,"isinstance(obj, list)") where funcname is the name of the function to be overloaded.

Whatever dispatch engine that is, is it not possible to do something more like when(funcname,{isinstance,{obj,list}))? (I used list syntax here as an example only (other syntaxes could work). I'm not sure if the 'obj' part is refering to a variable that would be in scope at the when declaration. That might have to be quoted as a string.

Regardless though, I'm pretty sure dispatch engines can use things other than interpreted strings.

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