On 31 Mar 2008 06:54:29 GMT, Marc 'BlackJack' Rintsch <[EMAIL PROTECTED]> wrote:
> On Sun, 30 Mar 2008 21:02:44 +0000, Jorgen Grahn wrote:
>
>> I realize this has to do with the extra read-ahead buffering documented for
>> file.next() and that I can work around it by using file.readline()
>> instead.
>>
>> The problem is, "for s in f" is the elegant way of reading files line
>> by line. With readline(), I need a much uglier loop. I cannot find a
>> better one than this:
>>
>> while 1:
>> s = sys.stdin.readline()
>> if not s: break
>> print '####', s ,
>>
>> And also, "for s in f" works on any iterator f -- so I have to choose
>> between two evils: an ugly, non-idiomatic and limiting loop, or one
>> which works well until it is used interactively.
>>
>> Is there a way around this? Or are the savings in execution time or
>> I/O so large that everyone is willing to tolerate this bug?
>
> You can use ``for line in lines:`` and pass ``iter(sys.stdin.readline,'')``
> as iterable for `lines`.
Thanks. I wasn't aware that building an iterator was that easy. The
tiny example program then becomes
#!/usr/bin/env python
import sys
f = iter(sys.stdin.readline, '')
for s in f:
print '####', s ,
It is still not the elegant interface I'd prefer, though. Maybe I do
prefer handling file-like objects to handling iterators, after all.
By the way, I timed the three solutions given so far using 5 million
lines of standard input. It went like this:
for s in file : 1
iter(readline, ''): 1.30 (i.e. 30% worse than for s in file)
while 1 : 1.45 (i.e. 45% worse than for s in file)
Perl while(<>) : 0.65
I suspect most of the slowdown comes from the interpreter having to
execute more user code, not from lack of extra heavy input buffering.
/Jorgen
--
// Jorgen Grahn <grahn@ Ph'nglui mglw'nafh Cthulhu
\X/ snipabacken.se> R'lyeh wgah'nagl fhtagn!
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