On a Linux Xeon server (x86_64) largefile support is (incorrectly)
not included.

configure determines:
checking size of int... 4
checking size of long... 8
checking size of void *... 8
checking size of short... 2
checking size of float... 4
checking size of double... 8
.
.
.
checking size of off_t... 8

but gets it wrong:

checking whether to enable large file support... no

To me it seems that the logic sizeof_off_t > sizeof_long
is wrong.

(I changed to comparison off_t > int and it built
with largefile support and works fine.)

$ uname -a
Linux cpu3 2.6.31-14-server #48-Ubuntu SMP Fri Oct 16 15:07:34 UTC 2009 x86_64 GNU/Linux

Ubuntu Lucid

The expression "largefile support" is a bit misleading. What it simply does is that it uses "long long" instead of "long" in order to store and compute file offsets. But, since a long is wide enough on your system to hold a off_t (both are 64 bits), it wouldn't make a difference. Your Python is already able to address files larger than 4GB, since it uses lseek() in all cases.

(so-called "largefile support" would be enabled if you compiled a 32-bit Python)

By the way, you can run:

$ ./python -m test.regrtest -v test_largefile

to check that the "large file" tests (> 2 GB) pass.