changing current dir and executing a shell script

[suresh]

Hi,
I want to execute the following command line stuff from inside python. 
$cd directory
$./executable

I tried the following but I get errors
import subprocess
subprocess.check_call('cd dir_name;./executable')

Due to filename path issues, I cannot try this version.
subprocess.check_call('./dir_name/executable')

Any suggestions?
thanks
suresh