[Python-Dev] redefining is

[Greg Ewing]

Andrew Koenig <ark-mlist at att.net>:

> There are certainly more than three meaningful forms of equivalence.  I
> claim, however, that these three forms already have special status in the
> language, because it is implementation-defined whether two occurrences of
> the same string literal refer to the same object.

But this special status is only spelled out for certain
fully-immutable objects, for which your "substitutability" relation is
equivalent to "==".

In all of this, I've yet to see a single use case put forward where it
would be *wrong* to use "==" instead of "substitutability", let alone
one frequently enough encountered to be worth adding a new operator or
changing the semantics of an existing one.

Greg Ewing, Computer Science Dept, +--------------------------------------+
University of Canterbury,	   | A citizen of NewZealandCorp, a	  |
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