One further data point.   On two rhel5 systems with identical kernels,
both x86_64, both python-2.4.3... basically, everything I've thought to
check identical, I ran the test code with f.read() in an infinite loop.
 One system only has one TCP socket in use at a time.  The other one has
multiple TCP sockets in use, but they all close eventually.

/usr/sbin/lsof -p INTERPRETER_PID|wc -l reported 

96 67 97 63 91 62 94 78

on subsequent runs.