lfs confusion

[John Hunter]

I am a bit confused about LFS in python.  In the olden days, I used
the following to test whether python and my kernel supported large
files

    >>> fd = open('/dev/null', 'rw')
    >>> fd.tell()
    0L

If 0L was returned, LFS was enabled, if 0 was returned, LFS was not
enabled.

I built python with LFS

  499  CFLAGS='-D_LARGEFILE64_SOURCE -D_FILE_OFFSET_BITS=64' OPT="-g -O2 $CFLAGS"         ./configure
  501  make
  502  make install

But fd.tell() returned 0.  I wrote a little script to create a large
file >4GB

    [root at crcdocs tmp]# cat lfs_write.py
    fd = file('test2.dat', 'w')

    SIZE = 4096
    STOP = 2**32
    total = 0
    s = 'a'*SIZE
    while total<STOP:
        fd.write(s)
        total += SIZE
        print total


    print fd.tell()


and it ran without incident, reporting at the end 4294967296 (no L).
So I can at least write files past the 2GB limit (and I wrote a script
to verify that I could read the who file too).  

I am installing a zope server and will need to create a Data.fs that
exceeds the 2GB limit.  

Is the fd.tell() 0L trick no longer valid.  What is the right way to
test for LFS support in python?

JDH