Warning about "for line in file:"
Just van Rossum
just at xs4all.nl
Wed Feb 20 15:55:10 EST 2002
In article <mailman.1014235657.26957.python-list at python.org>,
"Jason Orendorff" <jason at jorendorff.com> wrote:
> > This is highly unintuitive to me, indeed so much so that I would like to
> > call it a bug!
> I agree!
Heh, I was starting to think I'm the only one...
> This could be improved by having file.__iter__()
> always return the same object. But that doesn't solve the problem
> in full.
Still, it would be 100% better than the current situation.
> One possibility is to change file.__iter__() to return
> iter(file.readline, ''), and have users call file.xreadlines()
> explicitly, and accept the semantic oddness, if they need the
> extra speed. :-\
No, "for line in file" should become *the* idiom, and therefore it
should also be the fastest idiom.
> Another possible hack would be to have xreadlines.next() call
> file.seek() on the underlying file object, to make sure the two
> are in sync. That sounds like a pain to me.
I have no idea how expensive seek() is in general, but it would indeed
clear up the semantics. But what about the other way around? Should a
seek() also update the iterator? It's just really messy to have these
two states exist at the same time :-(.
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