human
I wrote the below code

    def get_journald_output():
        formatter = journald_json_formatter(output_file)
        ran = run_ssh(reactor=reactor, host=host, username='root', command=['journalctl', '--lines', '0', '--output', 'export', '--follow', '-u', 'docker', '-u', 'flocker-control', '-u', 'flocker-dataset-agent', '-u', 'flocker-container-agent', '-u', 'flocker-docker-plugin'], handle_stdout=formatter)
        ran.addErrback(write_failure, logger=None)
        ran.addCallback((lambda ignored: formatter('')))
        return ran
    return loop_until(reactor, get_journald_output, repeat(2.0))

What's a good function header?
 ... Here's a good function header?
assistant
#Here's a good function header.

def capture_journal(reactor, host, output_file):