Event classes （事件类）
An event class describes a Ryu event generated in the system.By convention, event class names are prefixed by "Event".Events are generated either by the core part of Ryu or Ryu applications.A Ryu application can register its interest for a specific type of event by providing a handler method using ryu.controller.handler.set_ev_cls decorator.
在系统中一个事件类描述一个Ryu事件的发生。按照惯例，事件类名字的前缀是Event。事件发生通过Ryu的核心部分或者是Ryu应用。一个Ryu应用根据事件类型一个处理方法使用ryu.controller.handler.set_ev_cls装饰器来注册一个刘某应用程序可以通过提供一种使用ryu.controller.handler.set_ev_cls装饰处理方法的一种特定类型的事件。
OpenFlow event classes （Openflow事件类）
ryu.controller.ofp_event module exports event classes which describe receptions of OpenFlow messages from connected switches.By convention, they are named as ryu.controller.ofp_event.EventOFPxxxxwhere xxxx is the name of the corresponding OpenFlow message.For example, EventOFPPacketIn for packet-in message.The OpenFlow controller part of Ryu automatically decodes OpenFlow messagesreceived from switches and send these events to Ryu applications which expressed an interest using ryu.controller.handler.set_ev_cls.OpenFlow event classes are subclasses of the following class. ryu.controller.ofp_event组件输出事件类描述接收Openflow信息从连接的交换机上。通常，他们命名例如ryu.controller.ofp_event.EventOFPxxxx where xxxx 是相应的OpenFlow消息的名字。例如，EventOFPPacketIn用来表示packe-in消息。Ryu的Openflow控制器部分自动解码从交换机收到的Openflow消息和发送这个事件给Ryu应用主要用ryu.controller.handler.set_ev_cls。Openflow事件类有一下几类子类
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class
ryu.controller.ofp_event.EventOFPMsgBase(msg) -
The base class of OpenFlow event class.是Openflow事件类的基类
OpenFlow event classes have at least the following attributes.OpenFlow事件类至少有以下属性。
Attribute Description msg An object which describes the corresponding OpenFlow message.一个对象，描述了相应的OpenFlow消息。 msg.datapath A ryu.controller.controller.Datapath instance which describes an OpenFlow switch from which we received this OpenFlow message.一个ryu.controller.controller.datapath实例描述了OpenFlow交换机，我们收到了OpenFlow的消息。 The msg object has some more additional members whose values are extracted from the original OpenFlow message.msg对象有一些额外的成员其值由原来的OpenFlow消息中提取
See OpenFlow protocol API Reference for more info about OpenFlow messages. 看OpenFlow protocol API Reference 获取更多关于Openflow消息的信息。