Popen - How can I read data before CTRL+C command is issued

[volcano63]

You can can try reading from self.proc.stdout till you get your device in the output - and then kill the process.

for line in self.proc.stdout:
    if <> in line:
        self.proc.kill()

(I think).

The problem is - it may get stuck. And what happens if the device never shows up?

I used to write stdout to a file stdout=open(<log name>, 'w') - and then periodically look-up the file content in a loop, and leaving the loop after some maximum number of attempts.