Throw the cat among the pigeons

[Terry Reedy]

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