This is what happens:

Traceback (most recent call last):
  File "/home/dewaard/Python/Antiqbook/executiontest.py", line 8, in ?
    print >>f, "foobar"
IOError: [Errno 9] Bad file descriptor

This is my code:

import os
import sys

command = ("ftpasswd --passwd --file=%s --name=%s --uid=%d --home=%s --shell=%s --gid=%d" %
("/etc/proftpd/passwd", "foo", 5001, "/ftp/aar", "/bin/false", 5000))

f = os.popen(command)
print >>f, "foobar"
f.close()