def ping(self):
<EOL>if not self.conn:<EOL><INDENT>self.connect()<EOL><DEDENT>self.conn.send('<STR_LIT>', time.time())<EOL>cmd, payload = self.conn.recv()<EOL>recv_ts = time.time()<EOL>if cmd != '<STR_LIT>':<EOL><INDENT>raise Exception("<STR_LIT>")<EOL><DEDENT>return recv_ts - payload[<NUM_LIT:0>]<EOL>
Ping the server.  Returns the time interval, in seconds,
required for the server to respond to the PING message.