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

[js]

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.