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To: python-list@python.org
From: Terry Reedy <tjreedy@udel.edu>
Subject: Re: Throw the cat among the pigeons
Date: Tue, 05 May 2015 19:22:55 -0400
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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 =E2=80=98tail recursive=E2=
=80=99 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=20
of recursion or the process of removing recursion. I wrote a tail=20
recursive function, and I believe you did too.

What Python does not have is automatic tail call optimization, or=20
specifically, tail recursion *elimination*. Both possibilities, the=20
general and specific, have been considered and rejected for excellent=20
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=20
different method.  That is not surprising.  Relative timings for CPython =

vary a few percent between different combinations of Python version, C=20
compiler and settings, operating system, and cpu and other hardware.

--=20
Terry Jan Reedy