Result of ``a is b''

[Asun Friere]

Skip Montanaro <skip at pobox.com> wrote in message news:<mailman.52.1079472192.742.python-list at python.org>...

> No, its behavior is quite well-specified.  It does a pointer comparison.
> Here is my "is" rule:
> 
>     Use "is" to compare two objects only if one is explicitly known to be a
>     singleton defined by the language (None, Ellipsis, True, False).
> 
> and its corrolary:
> 
>     Never use "is" to compare two programmer-defined variables.
>
What about when it is an object explicitly known to be singleton
defined by the programmer. ;)

Another possible use, would be to type test, eg.  'foo.__class__ is
Foo', bearing in mind that one should avoid type testing in favour of
polymorphism.