[Python-ideas] A Continuations Compromise in Python

[Robert Collins]

On Mon, 2009-05-04 at 00:34 +1000, Steven D'Aprano wrote:


> Okay, this toy program isn't exactly a mission-critical application, but 
> it does demonstrate a genuine performance penalty when using recursion. 
> In this case, two recursive calls (one of which is a tail-call) takes 
> nearly 60% more time than a single recursive call in a while loop.

This doesn't demonstrate where the issue is.

Is it function calls? The tail recursion call makes (eyeball count)
twice as many python function calls (not calls into generators) per call
to move(2)?


Or perhaps something else?

Sure, the TCO one is slower, but is the handing of result from generator
to generator really the issue? If it is rather something else, it may be
that the nested yielding while costing, is not costing
disproportionately - and is still a fraction of the cost.

python -m timeit 'from foo import do_move, do_move2' 'do_move()'
65535
10 loops, best of 3: 164 msec per loop

python -m timeit 'from foo import do_move, do_move2' 'do_move2()'
32768
10 loops, best of 3: 108 msec per loop

Half as many function calls, 2/3rds the time.

*Much* better measurement than these sketches is needed to say where the
issue is.

-Rob
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