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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