[Python-ideas] Revised**5 PEP on yield-from

Jacob Holm jh at improva.dk
Sat Feb 28 21:54:32 CET 2009

Replying to myself here...

Jacob Holm wrote:
> I think I can actually see a way to do it that should be fast enough, 
> but I'd like to
> work out the details first. If it works it will be O(1) with low 
> constants as long as
> you don't build trees, and similar to traversing a delegation chain in 
> the worst case.
> All this depends on getting it working using delegation chains first 
> though, as most of
> the StopIteration and Exception handling would be the same.

I have now worked out the details, and it is indeed possible to get O(1) 
for simple cases and amortized O(logN)
in general, all with fairly low constants. I have implemented the tree 
structure as a python module and added a trampoline-based pure-python 
implementation of "yield-from" to try it out.

It seems that this version beats a normal "for v in it: yield v" when 
the delegation chains get around 90 generators deep. This may sound like 
much, but keep in mind that this is all in python. I expect a C 
implementation of this would break even much sooner than that (hoping 
for <5). If you (or anyone else) is interested I can post the code here. 
(Or you can suggest a good place to upload it).



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