Chroot Jail Not Secure for Sandboxing Python?

[gregpinero at gmail.com]

This wiki page suggests using a chroot jail to sandbox Python, but
wouldn't running something like this in your sandboxed Python instance
still break you out of the chroot jail:

 os.execle ('/usr/bin/python','-c','import os; os.execlp("/bin/sh")',
{})

or maybe:

 del os.environ['LD_PRELOAD']
 os.execl ('/usr/bin/python','-c','import os; os.execlp("/bin/sh")')

My ISP suggested these as counter-examples to my request for a chroot
jail.  (I couldn't even get Python running in chroot to test this, nor
could I run these commands locally in Python on Ubuntu, though maybe
they opened sh?)

So is a chroot jail not adequate for sandboxing Python?

-Greg