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From: Terry Reedy <tjreedy@udel.edu>
Subject: Re: Guido rethinking removal of cmp from sort method
Date: Fri, 01 Apr 2011 14:57:48 -0400
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Xref: x330-a1.tempe.blueboxinc.net comp.lang.python:2381

On 4/1/2011 3:45 AM, Paul Rubin wrote:

> What happens then is you define a new interface.

Like key= versus cmp=

>  In Microsoft-speak if
> the IWhatever interface needs an incompatible extension like new
> parameters, they introduce IWhatever2 which supports the new parameters.
> They change the implementation of IWhatever so it becomes a wrapper for
> IWhatever2 setting the new parameters to default values, to keep
> implementing the old behavior.

If cmp had been left (or were reinstated) but its implementation changed 
internally to use cmp_to_key to make it a wrapper for key, you would be 
happy? 2to3 could probably gain a fixer to change

.sort(cmp=f) # to

import functools import cmp_to_key
.sort(key=functools.cmp_to_key(f))

I know some would not like this because interface change is not their 
real concern.

-- 
Terry Jan Reedy