[Python-Dev] redefining is (original) (raw)

Samuele Pedroni pedronis at bluewin.ch
Fri Mar 19 17:07:30 EST 2004

At 15:33 19.03.2004 -0500, Andrew Koenig wrote:

> Okay, but I don't see why that implementation detail is important.

It is important because it causes programs to behave differently on different implementations. > > So what I'm claiming is that there should be a way of asking: Given two > > objects, is there any way to distinguish them aside from their identity? > Why do you need to ask that question? Further more, why is it > important enough to require a builtin operator? It certainly doesn't require a builtin operator. I do think, however, that the proposed comparison is more useful than "is" in most contexts in which programmers use "is" today. In particular, programs that use "is" can easily contain bugs that testing on a particular implementation can never reveal, and using the proposed comparison instead makes such bugs much less likely (and perhaps even impossible).

maybe, OTOH I suspect that people most puzzled by

a = 1 b = 1 a is b True a = 99 b = 99 a is b True a = 101 b = 101 a is b False

really simply expect there to be just one 1 and 99 and 101, not an half-a-page definition of 'is' or some such involving the notion of (im)mutability.

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