Maric Michaud wrote:
> Le jeudi 12 avril 2007 10:34, Diez B. Roggisch a écrit :
>> I presume this is an OS thing. The first lines aren't communicated to
>> the process until either the file is closed - C-d - or the buffer the OS
>> puts before the stream is filled. You can switch to unbuffered behviour
>> somehow, google for it. Termios should be in your query.
>
> I don't know if this a python or OS thing, but I know that iterating over a
> file is not like applying successive call to readline method. You should try
> to use readline instead.
>
That, of course, is because files are iterators.
> The following work exactly the same on windows and Linux (python2.4) :
>
>>>> f=open('txt')
>>>> l=f.readline()
>>>> while(l) :
> ... print l,
> ... print "rest : " + f.read()
> ... l=f.readline()
> ...
> foo
> rest : bar
> baz
>
> works as expected, while :
>
>>>> f=open('txt')
>>>> for l in f :
> ... print l,
> ... print "rest : " + f.read()
> ...
> foo
> rest :
> bar
> rest :
> baz
> rest :
>
> doesn't, it seems that file iteratiion itself use a buffer. In python 2.5,
> you
> just can't do this :
>
> Python 2.5 (release25-maint, Dec 9 2006, 14:35:53)
> [GCC 4.1.2 20061115 (prerelease) (Debian 4.1.1-20)] on linux2
> Type "help", "copyright", "credits" or "license" for more information.
>>>> f=open('txt')
>>>> for l in f :
> ... print l,
> ... print "rest : " + f.read()
> ...
> foo
> Traceback (most recent call last):
> File "<stdin>", line 3, in <module>
> ValueError: Mixing iteration and read methods would lose data
>
But you *can* do this (untested):
for l in f:
print l,
print "rest:", f.next()
Of course there are always edge cases. In this particular instance I
suspect that the handling of files with odd numbers of lines might be
slightly different, but I can't work up enough enthusiasm to actually
run this code. The error method pretty much explains what the problem
is: you have to iterate over files or read them, you shouldn't try and
do both on the same file.
regards
Steve
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