xreadlines (was Re: while true: !!!)

Alex Martelli aleaxit at yahoo.com
Fri Dec 15 15:38:29 CET 2000

"Jeff Epler" <jepler at inetnebr.com> wrote in message
news:slrn93k8sn.lb.jepler at potty.housenet...
> On Thu, 14 Dec 2000 11:14:38 +0100, Alex Martelli
>  <aleaxit at yahoo.com> wrote:
> >...if it was able to iterate over already-opened file-like objects,
> >than having to open actual files itself, it WOULD conceptually solve it
> >all.  I wonder how hard it would be to generalize fileinput in this
way --
> >probably not very (the in-place-rewriting option would be incompatible
> >with having already-opened file-like objects in the list, of course).
> xreadlines takes a file object, not a filename, as its argument.

Good for it (what IS it?-), but I was talking about the fileinput
module; I thought it would be nice for the user to generalize the
functionality (and enhance the speed) of fileinput, rather than
introducing a completely new and separate module.

> >If [using readline] was a performance problem, it could of course
> >also be fixed in a future fileinput version without changing code that
> >uses it (again, in-place-rewriting would probably have to inhibit the
> >optimization, although that isn't entirely clear).
> xreadlines internally uses fp.readlines(sizehint), so
> for line in xreadlines.xreadlines(fp): pass
> is just about as fast as
> for line in fp.readlines(): pass
> except that it will not require storage for the whole file.

Now *THAT* is interesting indeed!  The closest I got was about
a 2:1 ratio, in the LinesOf class which I posted today -- using
the same technique.  I wonder what optimizations I missed that
would allow twice-as-good performance as that!  Do tell, it's
always nice to learn little (or big) tricks like that...!


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