spliting on ":"

Bryan Olson fakeaddress at nowhere.org
Mon Mar 6 18:11:46 CET 2006


Peter Hansen wrote:
> The archives could tell you more, but basically on is usually interested 
> in *identity* with a singleton object (None), not in whether the object 
> on is examining happens to compare equal.  A custom object could be 
> designed to compare equal to None in certain cases, even though it *is 
> not* None, leading to the "== None" approach being defective code.

But if a custom class allows instances to compare as equal to None,
we might reasonably expect the programmers had a reason. There's not 
much anyone can do with None besides passing it around and comparing
it by value or identity. Insisting on 'is' rather than '==' will break
whatever polymorphism such a custom object was trying to achieve.


> In the specific code in question, it won't make any differences, but I 
> pointed it out to help folks who don't know this to start developing the 
> safer habit, which is always to use "is" and "is not" with None (or, 
> generally, with other singletons).

Hmmm... To make my code safer, I'm thinking I should replace doc strings
that say "if bluf is Null" with "if blurf compares equal to Null".


-- 
--Bryan




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