[Python-Dev] The iterator story

[Greg Ewing]

> Should people prefer to write:
> 
>     for item from iterator:
>         do something
> 
> when they only need to loop over something once?

This shows up a problem with Ping's proposal, I think:
The place where you write the for-loop isn't the place
where you know whether something will be iterated over
more than once or not. How is a library routine going
to know whether a sequence passed to it is going to
be used again later? It's impossible -- global knowledge
of the whole program is needed.

This appears to leave the library writer with two
choices: (1) Use for-in, to be on the safe side,
in case the user doesn't want the sequence destroyed --
but then it can't be used on a destructive iterator, 
even if the caller knows he won't be using it again;
(2) use for-from, and force everyone who calls it to
adapt sequences to iterators before calling.

Either way, things get messy and complicated and
possibly dangerous.

Greg Ewing, Computer Science Dept, +--------------------------------------+
University of Canterbury,	   | A citizen of NewZealandCorp, a	  |
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