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

[maffaz]

I have a command line tool in windows that scans for devices.

It will loop through all devices in range repeating until it receives a CTRL+C command.

device1 name firmware
device2 name firmware
device3 name firmware
device1 name firmware
device2 name firmware
device3 name firmware
...

I want to stop the scan when it reaches a certain device so I can issue an update firmware command.

At the moment I can only capture the output after the CTRL+C command is issued using the following function that starts the scan, sleeps, then issues the CTRL+C command, I then catch the error and process the output in the except block:

            command = [self.cli_tool, '-s']

            startupinfo = subprocess.STARTUPINFO()
            startupinfo.dwFlags |= subprocess.STARTF_USESHOWWINDOW
            startupinfo.wShowWindow = subprocess.SW_HIDE

            stream = []

            if self.check_dongle_firmware() is not False:
                try:                    
                    self.proc = subprocess.Popen(
                                command, 
                                stdin=subprocess.PIPE, 
                                stdout=subprocess.PIPE, 
                                stderr=subprocess.DEVNULL, 
                                startupinfo=startupinfo)

                    time.sleep(SCAN_TIMEOUT)
                    os.kill(self.proc.pid, signal.CTRL_C_EVENT)
                    self.proc.wait()

                except KeyboardInterrupt:                
                    for line in self.proc.stdout:
                        stream.append(line)							

                    for x in stream[7:]:
                        x = x.decode()
                        print(x.strip())   

I want something like this:

    stream = []

     self.proc = subprocess.Popen(
                                command, stdin=subprocess.PIPE,
                                stdout=subprocess.PIPE, 
                                stderr=subprocess.DEVNULL, 
                                startupinfo=startupinfo)

    for line in self.proc.stdout:
        stream.append(line)	
		if 'device' in line:
			os.kill(self.proc.pid, signal.CTRL_C_EVENT)
			self.proc.wait()

This does not work though.

I tried various combinations using :

universal_newlines=True

bufsize=1

self.proc.communicate()[0]

When I try the code using a command like ping I have no problem and full control of the output.

I have searched SO for tried anything that looks similar but nothing works for what I need.

I think I am missing something obvious or it is not possible due to the tool locking or being in a separate process not accessible by python.

Any direction or advice is appreciated!