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

[nilamo]

You could read the stdout of the process, and when there's nothing left to read you know it's "ready"?

Here's some fake code I didn't test:

proc = subprocess.Popen(exe_path, stdout=subprocess.PIPE)
while proc.stdout.peek():
   output = proc.stdout.read()
# no more output (or we read input before the process wrote anything)