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

Guido van Rossum guido at python.org
Sat Jul 21 17:16:12 CEST 2007

On 7/21/07, Joe Smith <unknown_kev_cat 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?

-- --Guido van Rossum (home page: http://www.python.org/~guido/)

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