yield_all needed in Python

[David Eppstein]

In article <lcacpnxp8s.fsf at gaffa.mit.edu>,
 Douglas Alan <nessus at mit.edu> wrote:

> > Cetainly, if <yield_all
> > iterator> == <for i in iterator: yield i>, I don't see how anything
> > is gained except for a few keystrokes.
> 
> What's gained is making one's code more readable and maintainable,
> which is the one of the primary reasons that I use Python.

I don't see a lot of difference in readability and maintainability 
between the two versions.  And if yield_all is going to expand into the 
loop, anyway, I'd prefer to make that obvious by using the for-loop 
version, rather than using a keyword and pretending that passing the 
iterators on has no overhead.

If we're talking about machinery behind the scenes to shortcut chains of 
yield_all's, so that the time to pass items up through the chain is 
smaller than it would be in the for-loop case, I'd think that would be a 
better reason for a keyword, because it's not something that can be done 
very easily without one in the current language.  I don't know how to 
make such shortcutting machinery faster than logarithmic in the worst 
case (taking into account the possibility that multiple generators could 
have yield_all's to the same iterator) but I think it could be made 
nearly constant time in most situations.  On the other hand, I'm not 
convinced that this would be needed frequently enough to warrant the 
complexity of trying to optimize it.

-- 
David Eppstein
Computer Science Dept., Univ. of California, Irvine
http://www.ics.uci.edu/~eppstein/