[Python-Dev] Single- vs. Multi-pass iterability

[Guido van Rossum]

> > No.  I won't have "for line in file" be slower than attainable.
> 
> +1.  I _intensely_ want to be able to teach beginners to use "for line in 
> file" and have it be fast in the common case.  "Nice" behavior for rarer 
> cases of prematurely interrupted loops is OK, if feasible, but secondary.  
> Having "for line in file" play nicely with other method calls on 'file' has 
> no importance to me in this context -- no more than, e.g., having "for item 
> in alist" play nicely with calls to mutating methods of object alist.

Exactly.

> > The only solution I accept is a complete rewrite of the I/O system
> > without using stdio, so xreadlines can be integrated.
> 
> I thought Just's suggestion (about having the file object remember
> the xreadlines object in use, so that another for loop would continue
> right where the first one exited) seemed like a reasonable hack -- a
> compromise of reasonably little effort for some small secondary gain.

Oops, I missed that.  That seems reasonable indeed.

> Guess I must be missing something?  Of course the "complete rewrite"
> is an alluring prospect -- for many other reasons, such as enabling
> user control of file buffering in cross-platform ways, *yum* -- but it's not 
> going to happen in time for 2.3 anyway, is it?

I'm not going to hold up the 2.3 release, but if a patch lands in the
SF patch manager, I'm not going to reject it.  Hint, hint. :-)

--Guido van Rossum (home page: http://www.python.org/~guido/)