file.read() returns an emtpy even if its currenet position is not at the end

[js]

Thank you for reply.

I've just found the bug report on this.
http://sourceforge.net/tracker/index.php?func=detail&aid=1523853&group_id=5470&atid=105470

Nobody seems to be working on this,  though.

On 22 Apr 2007 14:41:29 -0700, Alberto Valverde <alberto at toscat.net> wrote:
> On Apr 22, 6:51 pm, "js " <ebgs... at gmail.com> wrote:
> > Hi list.
> >
> > I'm writing a tail -f like program in python
> > and I found file.read() doesn't work as I think it should.
> >
> > Here's the code illustrating my problem.
> >
> > ###
> > #!/usr/bin/env python
> > import os, sys
> > filename = "test.out"
> >
> > f = open(filename, "w+")
> > f.write("Hello")
> > f.flush()
> >
> > f.seek(0, 2)
> >
> > statinfo = os.stat(filename)
> > print "file size: %d" % statinfo.st_size
> > print "position : %d" % f.tell()
> > line = f.read()
> > print "line     : [%s]" % line
> >
> > # Writing the same file using another fd
> > f2 = open(filename, "a+")
> > f2.write("World")
> > f2.flush()
> > f2.close()
> >
> > statinfo = os.stat(filename)
> > print "file size: %d" % statinfo.st_size
> > print "position : %d" % f.tell()
> > line = f.read() # read() returns emtpy!! readlines?() works ok
> > ###
> >
> > Running the above, I got the following.
> > ###
> > file size: 5
> > position : 5
> > line     : []
> > file size: 10
> > position : 5
> > ###
> >
> > So my question is
> > why the second f.read() returns an emtpy?>From tell() and its st_size I'm sure that file descriptor is not at the EOF
> >
> > and read()'s doc says
> > "An empty string is returned when EOF is encountered immediately".
> > Using readline() or readlines() instead of read() works great though.
> >
> > I'm using  Python  2.4.3 on OS X.
> >
> > Probably I'm missing something but I could't figure out.
> >
> > Thanks in advance.
>
> I've hit into the same issue recently when implementing more or less
> the same thing and found that doing f.seek(f.tell()) on the file
> object when empty strings start to come out allows you to continue
> read()ing after hitting EOF if the file grows again.
>
> I finally dropped the "hack" and used readline instead since it made
> me a little bit uneasy though...
>
> Alberto
>
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>