import subprocess

echo = subprocess.Popen(['echo','123'],
                        stdout=subprocess.PIPE,
                        )

sudo = subprocess.Popen(['sudo','-S','iptables','-L'],
                        stdin=echo.stdout,
                        stdout=subprocess.PIPE,
                        )

end_of_pipe = sudo.stdout

print "Iptables Chains:"
print end_of_pipe.read()