Are there any list comparison optimizations in Python?

Huaiyu Zhu huaiyu at gauss.almadan.ibm.com
Wed Nov 14 22:59:44 CET 2001


On Wed, 14 Nov 2001 07:32:07 -0800, Emile van Sebille <emile at fenx.com> wrote:
>
>"Huaiyu Zhu" <huaiyu at gauss.almadan.ibm.com> wrote in message
>news:slrn9v2qc7.1ss.huaiyu at gauss.almadan.ibm.com...
>>
>> class A:
>>    def __cmp__(a,b): return -1
>>
>> a = [A()]*3
>> a == a            # returns 0
>> a is a            # returns 1
>>
>>
>> Is this intended?
>
>Yes, as decreed by the author of class A.
>
>
> I would think that mandating
>>     a is b  implies  a == b
>> would make programs easier to read.
>>
>
>Because it's in the class that way, you'd have to assume the author knew
>what was intended.

I made up the example just to show the issue.  Can someone think of a real
world example where this is useful?  If it's not like this until recently,
was it a feature missed by users in the past?  Is the special case
introduced by NaN worth changing the behvior in all the other cases?

Huaiyu



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