Execv'ing processes is OK as long as you don't fork:
__import__("os").execv("/usr/bin/uname", ["uname", "-a"])
Linux ip-10-196-3-111 2.6.32-amazon-xen-r3 #1 SMP Mon Jan 16 21:03:16 PST 2012 i686 GNU/Linux
As for the actual files, there are a few clues that a chroot is created for every request : /proc is not mounted, /etc is minimal (root + 1 user in passwd) and "ls -id /" returns a new inode number every time.
adam.py... :) If only I knew more about bytecode...
pp = pprint.PrettyPrinter(depth=6)
f = inspect.currentframe()
c = 0
while f is not None:
c += 1
if c == 20:
f = f.f_back