Lazy "for line in f" ?

Miles semanticist at gmail.com
Sun Jul 22 19:21:32 CEST 2007


On 7/22/07, Alexandre Ferrieux <alexandre.ferrieux at gmail dot com> wrote:
> The Tutorial says about the "for line in f" idiom that it is "space-
> efficient".
> Short of further explanation, I interpret this as "doesn't read the
> whole file before spitting out lines".
> In other words, I would say "lazy". Which would be a Good Thing, a
> much nicer idiom than the usual while loop calling readline()...
>
> But when I use it on the standard input, be it the tty or a pipe, it
> seems to wait for EOF before yielding the first line.

It doesn't read the entire file, but it does use internal buffering
for performance.  On my system, it waits until it gets about 8K of
input before it yields anything.  If you need each line as it's
entered at a terminal, you're back to the while/readline (or
raw_input) loop.

-Miles



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