[Python-Dev] basenumber redux (original) (raw)
Raymond Hettinger python at rcn.com
Thu Jan 19 07:55:42 CET 2006
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-----Original Message----- From: python-dev-bounces+python=rcn.com at python.org [mailto:python-dev-_ _bounces+python=rcn.com at python.org] On Behalf Of Martin v. Löwis Sent: Wednesday, January 18, 2006 3:36 PM To: Jason Orendorff Cc: python-dev at python.org Subject: Re: [Python-Dev] basenumber redux
Jason Orendorff wrote: > Really this is just further proof that type-checking is a royal pain > in Python. Or rather, it's not hard to cover the builtin and stdlib > types, but it's hard to support "duck typing" too. Are we going about > this the right way? It's not as bad. There is nothing wrong with restricting the set of acceptable types if callers would have no problems to convert their input into one of the acceptable types.
Somehow my earlier post on this thread didn't seem to take.
There are problems for callers converting their inputs:
currently existing number-like objects would need be retro-fitted with a new base class and possibly change their behavior from old-style to new-style.
some useful classes (such as a symbolic type) already inherit from str. That prevents them from also being able to inherit from basenumber.
I'm -1 on the proposal because the benefits are dubious (at best it simplifies just a handful of code fragments); it adds yet another API to learn and remember; it is darned inconvenient for existing code seeking to emulate number-like behavior; and it precludes number emulation for classes that already have a built-in base class.
For the most part, functions that enforce type checking are up to no good and make life harder for their callers. If Python ultimately grows interfaces, I hope they remain optional; as soon as functions start insisting on interface checking, then it will spread like cancer. The basenumber proposal is essentially a step down that slippery slope.
Raymond
Raymond
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