<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def check_ports_on_br(self, bridge='br-ex', ports=['eth3']):
 """Check ports exist on bridge. ovs-vsctl list-ports bridge """

        LOG.info("RPC: check_ports_on_br bridge: %s, ports: %s" %
                 (bridge, ports))
        cmd = ['ovs-vsctl', 'list-ports', bridge]
        stdcode, stdout = agent_utils.execute(cmd, root=True)
        data = dict()
        if stdcode == 0:
            for port in ports:
                if port in stdout:
                    data[port] = True
                    stdout.remove(port)
                else:
                    data[port] = False
            return agent_utils.make_response(code=stdcode, data=data)
        # execute failed.
        message = stdout.pop(0)
        return agent_utils.make_response(code=stdcode,
                                         message=message)