How do you wait for a daemon to reach a certain state with subprocess.popen()?

[phalse]

Hello All,
I am trying to launch a daemon using subprocessor.Popen(), the daemon runs for about 30 seconds until it reaches a steady state.  My question is how can I determine it has reached the steady state before continuing my python execution?  
The daemon stops printing to screen once it has reached a steady state.  
Any help is appreciated, I don't have to use Popen if there are other better options.
Thanks!

try:
     p = subprocess.Popen(exe_path)
     #wait until it reaches steady state
     do_stuff()
except subprocess.CalledProcessError as e:
    print(e)
finallly:
    p.kill()