how to convert code that uses cmp to python3

[Steven D'Aprano]

On Fri, 8 Apr 2016 05:45 pm, Antoon Pardon wrote:

> Op 07-04-16 om 23:08 schreef Ben Finney:
>> Antoon Pardon <antoon.pardon at rece.vub.ac.be> writes:
>>
>>> With this method I have to traverse the two tuples almost always
>>> twice. Once to find out if they are equal and if not a second time to
>>> find out which is greater.
>> You are essentially describing the new internal API of comparison
>> operators. That's pretty much unavoidable.
> 
> And nobody thought about this kind of cases or found them important
> enough?

Probably not.

But you know, if you can demonstrate a genuine and severe slowdown with no
easy work-around, you should report it as a bug. It wouldn't be the first
time that functions removed from Python 3 have been re-added because it
turned out that they were needed.



>> If you want to avoid repeating an expensive operation – the computation
>> of the comparison value for an object – you could add an LRU cache to
>> that function. See ‘functools.lru_cache’.
> 
> I'll have a look.

I would be stunned if tuple comparisons with only a handful of values were
slow enough that its worth caching their results with an lru_cache. But try
it, and see how you go.




-- 
Steven