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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _determine_username(self, ip):
 """SSH in as root and determine the username."""

        ssh = subprocess.Popen([
            "ssh",
            "-o", "UserKnownHostsFile=/dev/null",
            "-o", "StrictHostKeyChecking=no",
            "root@%s" % ip],
            stdin=subprocess.DEVNULL,
            stdout=subprocess.PIPE,
            stderr=subprocess.DEVNULL)
        first_line = ssh.stdout.readline()
        ssh.kill()
        ssh.wait()
        if first_line:
            match = re.search(
                r"Please login as the user \"(\w+)\" rather than "
                r"the user \"root\".", first_line.decode('utf-8'))
            if match:
                return match.groups()[0]
        else:
            return None