Re: Guido rethinking removal of cmp from sort method

From	Terry Reedy <tjreedy@udel.edu>
Subject	Re: Guido rethinking removal of cmp from sort method
Date	2011-04-01 15:37 -0400
References	(2 earlier) <JfVkp.5068$sS4.4758@newsfe11.iad> <4d94326c$0$30003$c3e8da3$5496439d@news.astraweb.com> <R1elp.6224$sP1.5155@newsfe07.iad> <mailman.67.1301639410.2990.python-list@python.org> <7x8vvue7or.fsf@ruckus.brouhaha.com>
Newsgroups	comp.lang.python
Message-ID	<mailman.94.1301686668.2990.python-list@python.org> (permalink)

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

> What happens then is you define a new interface.  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.

Now you have two versions, and eventually many more, to maintain and 
document. That takes resources we currently do not have.

Some problems in addition to the benefits of this approach:
1. The users of IWhatever will not gain the benefits of IWhatever2.
2. Upgrading to IWhatever2 requires a change of name as well as off 
parameters.
3. If only some users are upgraded, the IWhatever and IWhatever2 users 
may become incompatible even though they were before, thus breaking code 
without changing the old interface.

Example: Python2 added str2 (= unicode) on top of str. This had all the 
problems listed above. Since CPython uses str internally, in particular 
for identifiers, CPython users were stuck with the limitations of str. 
Rebinding str to mean str2 has many benefits, especially in the future, 
in addition to current costs.

-- 
Terry Jan Reedy

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Re: Guido rethinking removal of cmp from sort method harrismh777 <harrismh777@charter.net> - 2011-03-31 01:34 -0500
  Re: Guido rethinking removal of cmp from sort method Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-03-31 07:51 +0000
    Re: Guido rethinking removal of cmp from sort method harrismh777 <harrismh777@charter.net> - 2011-04-01 01:13 -0500
      Re: Guido rethinking removal of cmp from sort method Chris Angelico <rosuav@gmail.com> - 2011-04-01 17:30 +1100
        Re: Guido rethinking removal of cmp from sort method Paul Rubin <no.email@nospam.invalid> - 2011-04-01 00:45 -0700
          Re: Guido rethinking removal of cmp from sort method Terry Reedy <tjreedy@udel.edu> - 2011-04-01 12:59 -0400
          Re: Guido rethinking removal of cmp from sort method Terry Reedy <tjreedy@udel.edu> - 2011-04-01 14:57 -0400
            Re: Guido rethinking removal of cmp from sort method Paul Rubin <no.email@nospam.invalid> - 2011-04-01 12:22 -0700
              Re: Guido rethinking removal of cmp from sort method Terry Reedy <tjreedy@udel.edu> - 2011-04-01 22:21 -0400
              Re: Guido rethinking removal of cmp from sort method Antoon Pardon <Antoon.Pardon@rece.vub.ac.be> - 2011-04-04 11:34 +0200
                Re: Guido rethinking removal of cmp from sort method Lie Ryan <lie.1296@gmail.com> - 2011-04-04 23:35 +1000
                Re: Guido rethinking removal of cmp from sort method Terry Reedy <tjreedy@udel.edu> - 2011-04-04 13:26 -0400
                Re: Guido rethinking removal of cmp from sort method Terry Reedy <tjreedy@udel.edu> - 2011-04-04 15:05 -0400
              Re: Guido rethinking removal of cmp from sort method Terry Reedy <tjreedy@udel.edu> - 2011-04-04 13:22 -0400
          Re: Guido rethinking removal of cmp from sort method Terry Reedy <tjreedy@udel.edu> - 2011-04-01 15:37 -0400
            Re: Guido rethinking removal of cmp from sort method Paul Rubin <no.email@nospam.invalid> - 2011-04-01 14:37 -0700
              Re: Guido rethinking removal of cmp from sort method Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-04-02 00:42 +0000
                Re: Guido rethinking removal of cmp from sort method Paul Rubin <no.email@nospam.invalid> - 2011-04-01 19:31 -0700
              Re: Guido rethinking removal of cmp from sort method Benjamin Peterson <benjamin@python.org> - 2011-04-02 03:31 +0000
                Re: Guido rethinking removal of cmp from sort method Paul Rubin <no.email@nospam.invalid> - 2011-04-01 20:43 -0700
            Re: Guido rethinking removal of cmp from sort method Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-04-02 10:13 +0000
              Re: Guido rethinking removal of cmp from sort method rantingrick <rantingrick@gmail.com> - 2011-04-04 14:10 -0700
                Re: Guido rethinking removal of cmp from sort method Chris Angelico <rosuav@gmail.com> - 2011-04-05 07:41 +1000
                Re: Guido rethinking removal of cmp from sort method rantingrick <rantingrick@gmail.com> - 2011-04-04 15:16 -0700
                Re: Guido rethinking removal of cmp from sort method Chris Angelico <rosuav@gmail.com> - 2011-04-05 08:36 +1000
                Re: Guido rethinking removal of cmp from sort method Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-04-05 00:47 +0000
                Re: Guido rethinking removal of cmp from sort method harrismh777 <harrismh777@charter.net> - 2011-04-04 17:09 -0500
                Re: Guido rethinking removal of cmp from sort method Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-04-04 23:25 +0000
                Re: Guido rethinking removal of cmp from sort method harrismh777 <harrismh777@charter.net> - 2011-04-04 20:16 -0500
                Re: Guido rethinking removal of cmp from sort method Terry Reedy <tjreedy@udel.edu> - 2011-04-05 00:54 -0400
      Re: Guido rethinking removal of cmp from sort method Terry Reedy <tjreedy@udel.edu> - 2011-04-01 13:06 -0400
        Re: Guido rethinking removal of cmp from sort method Paul Rubin <no.email@nospam.invalid> - 2011-04-01 12:28 -0700
        Re: Guido rethinking removal of cmp from sort method harrismh777 <harrismh777@charter.net> - 2011-04-01 23:54 -0500
          Re: Guido rethinking removal of cmp from sort method Chris Angelico <rosuav@gmail.com> - 2011-04-02 16:06 +1100
            Re: Guido rethinking removal of cmp from sort method harrismh777 <harrismh777@charter.net> - 2011-04-02 00:17 -0500
              Re: Guido rethinking removal of cmp from sort method Chris Angelico <rosuav@gmail.com> - 2011-04-02 17:17 +1100
                Re: Guido rethinking removal of cmp from sort method harrismh777 <harrismh777@charter.net> - 2011-04-02 03:29 -0500
                Re: Guido rethinking removal of cmp from sort method Brian Quinlan <brian@sweetapp.com> - 2011-04-02 22:14 +1100
                Re: Guido rethinking removal of cmp from sort method harrismh777 <harrismh777@charter.net> - 2011-04-03 00:30 -0500
                Re: Guido rethinking removal of cmp from sort method geremy condra <debatem1@gmail.com> - 2011-04-02 22:46 -0700
                Re: Guido rethinking removal of cmp from sort method harrismh777 <harrismh777@charter.net> - 2011-04-03 02:17 -0500
                Re: Guido rethinking removal of cmp from sort method Brian Quinlan <brian@sweetapp.com> - 2011-04-03 16:36 +1000
                Re: Guido rethinking removal of cmp from sort method Terry Reedy <tjreedy@udel.edu> - 2011-04-02 22:14 -0400
                Re: Guido rethinking removal of cmp from sort method harrismh777 <harrismh777@charter.net> - 2011-04-03 00:26 -0500
                Re: Guido rethinking removal of cmp from sort method Terry Reedy <tjreedy@udel.edu> - 2011-04-04 01:38 -0400
          Re: Guido rethinking removal of cmp from sort method Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-04-02 09:39 +0000
            Re: Guido rethinking removal of cmp from sort method harrismh777 <harrismh777@charter.net> - 2011-04-03 00:09 -0500
  Re: Guido rethinking removal of cmp from sort method Terry Reedy <tjreedy@udel.edu> - 2011-03-31 11:26 -0400
    Re: Guido rethinking removal of cmp from sort method harrismh777 <harrismh777@charter.net> - 2011-04-01 01:44 -0500
      Re: Guido rethinking removal of cmp from sort method Terry Reedy <tjreedy@udel.edu> - 2011-04-01 15:13 -0400
        Re: Guido rethinking removal of cmp from sort method John Bokma <john@castleamber.com> - 2011-04-01 13:42 -0600
          Re: Guido rethinking removal of cmp from sort method Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2011-04-02 00:58 +0000
        Re: Guido rethinking removal of cmp from sort method harrismh777 <harrismh777@charter.net> - 2011-04-02 00:07 -0500

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