[Python-Dev] basenumber redux (original) (raw)

"Martin v. Löwis" martin at v.loewis.de
Mon Jan 16 07:39:41 CET 2006

Alex Martelli wrote:

I'll be happy to draft a PEP if needed (and just as happy to eventually provide an implementation patch if the PEP's accepted), but wanted to doublecheck on the general issue first!

Please do so. I've browsed somewhat through past discussions, but wasn't able to find a proposed specification of basenumber. Also, I only found half of a rationale for it: it is meant to be used along with isinstance, but I couldn't find out why you wanted to do that. In

http://mail.python.org/pipermail/python-dev/2003-November/039916.html

you explain that you wanted to multiply all items of self with other if other is a number; why couldn't this be written as

def mul(self, other): try: return self.class([ x*other for x in self.items ]) except TypeError: # various other multiplication cases

You give performance as the rationale; this is unconvincing as it would rather indicate that performance of exceptions should be improved (also, I think it is unpythonic to change the language for performance reasons, except in really common cases).

Also, in that example, I wonder if the use of multiplication is flawed. If you have so many multiplication cases, perhaps you abuse the notion of multiplication? Users will need to understand the different cases, as well, and they will be surprised when it works in one case, but not in a (seemingly similar) othercase.

Regards, Martin

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