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Re: Throw the cat among the pigeons

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On 5/5/2015 5:12 PM, Cecil Westerhof wrote:
> Op Tuesday 5 May 2015 22:46 CEST schreef Terry Reedy:
>
>>> Well, I did not write many tail recursive functions. But what
>>> surprised me was that for large values the ‘tail recursive’ version
>>> was more efficient as the iterative version.
>>
>> In your first thread, what you mislabelled 'tail recursive version'
>> was an iterative while loop version
>
> That is because Python has no tail recursion,

Yes is does. Please stop using 'tail recursion' to refer to the absence 
of recursion or the process of removing recursion. I wrote a tail 
recursive function, and I believe you did too.

What Python does not have is automatic tail call optimization, or 
specifically, tail recursion *elimination*. Both possibilities, the 
general and specific, have been considered and rejected for excellent 
reasons. I hinted at some of them in my post.

See https://en.wikipedia.org/wiki/Tail_call
for 'tail recursion' and 'tail call elimination'

What I believe you showed is that a while loop can be faster than a more 
or less equivalent for loop that produces the same result by a slightly 
different method.  That is not surprising.  Relative timings for CPython 
vary a few percent between different combinations of Python version, C 
compiler and settings, operating system, and cpu and other hardware.

-- 
Terry Jan Reedy

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Thread

Throw the cat among the pigeons Cecil Westerhof <Cecil@decebal.nl> - 2015-05-02 16:20 +0200
  Re: Throw the cat among the pigeons Cecil Westerhof <Cecil@decebal.nl> - 2015-05-03 17:12 +0200
    Re: Throw the cat among the pigeons Paul  Moore <p.f.moore@gmail.com> - 2015-05-05 08:47 -0700
      Re: Throw the cat among the pigeons Cecil Westerhof <Cecil@decebal.nl> - 2015-05-05 18:18 +0200
        Re: Throw the cat among the pigeons Dave Angel <davea@davea.name> - 2015-05-05 14:45 -0400
          Re: Throw the cat among the pigeons Cecil Westerhof <Cecil@decebal.nl> - 2015-05-05 21:42 +0200
            Re: Throw the cat among the pigeons Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-06 12:57 +1000
              Re: Throw the cat among the pigeons Chris Angelico <rosuav@gmail.com> - 2015-05-06 14:03 +1000
        Re: Throw the cat among the pigeons Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-05 14:30 -0600
        Re: Throw the cat among the pigeons Terry Reedy <tjreedy@udel.edu> - 2015-05-05 16:46 -0400
          Re: Throw the cat among the pigeons Cecil Westerhof <Cecil@decebal.nl> - 2015-05-05 23:12 +0200
            Re: Throw the cat among the pigeons Terry Reedy <tjreedy@udel.edu> - 2015-05-05 19:22 -0400
        Re: Throw the cat among the pigeons Dave Angel <davea@davea.name> - 2015-05-05 17:00 -0400
        Re: Throw the cat among the pigeons Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-05 15:23 -0600
          Re: Throw the cat among the pigeons Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-06 11:27 +1000
            Re: Throw the cat among the pigeons Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-05 23:58 -0600
              Re: Throw the cat among the pigeons Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-06 17:08 +1000
                Re: Throw the cat among the pigeons Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-06 10:17 -0600
                Re: Throw the cat among the pigeons Mark Lawrence <breamoreboy@yahoo.co.uk> - 2015-05-06 21:23 +0100
        Re: Throw the cat among the pigeons Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-05 15:39 -0600
        Re: Throw the cat among the pigeons Dave Angel <davea@davea.name> - 2015-05-05 17:55 -0400
        Re: Throw the cat among the pigeons Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-06 12:19 +1000
  Re: Throw the cat among the pigeons Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-06 14:05 +1000
    Re: Throw the cat among the pigeons Steven D'Aprano <steve+comp.lang.python@pearwood.info> - 2015-05-06 16:26 +1000
      Re: Throw the cat among the pigeons Dave Angel <davea@davea.name> - 2015-05-06 09:12 -0400
        Re: Throw the cat among the pigeons Dan Sommers <dan@tombstonezero.net> - 2015-05-07 03:16 +0000
      Re: Throw the cat among the pigeons Chris Angelico <rosuav@gmail.com> - 2015-05-06 23:55 +1000
      Re: Throw the cat among the pigeons Dave Angel <davea@davea.name> - 2015-05-06 10:22 -0400
      Re: Throw the cat among the pigeons Paul Rubin <no.email@nospam.invalid> - 2015-05-06 08:12 -0700
        Re: Throw the cat among the pigeons Alain Ketterlin <alain@universite-de-strasbourg.fr.invalid> - 2015-05-06 17:36 +0200
          Re: Throw the cat among the pigeons Dave Angel <davea@davea.name> - 2015-05-06 16:23 -0400
            Re: Throw the cat among the pigeons Alain Ketterlin <alain@universite-de-strasbourg.fr.invalid> - 2015-05-07 11:14 +0200
              Re: Throw the cat among the pigeons Chris Angelico <rosuav@gmail.com> - 2015-05-07 19:38 +1000
        Re: Throw the cat among the pigeons Ian Kelly <ian.g.kelly@gmail.com> - 2015-05-06 09:47 -0600
          Re: Throw the cat among the pigeons Paul Rubin <no.email@nospam.invalid> - 2015-05-06 10:24 -0700

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