<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def pbm(self):
 """ Plumbum lazy property """

        if not self.disable_rpyc:
            from plumbum import SshMachine
            return SshMachine(host=self.private_hostname, user=self.username,
                              keyfile=self.key_filename,
                              ssh_opts=["-o", "UserKnownHostsFile=/dev/null",
                                        "-o", "StrictHostKeyChecking=no"])
        else:
            return None