NameError: 全局名称 'get_all_switch' 未定义

Question

我刚开始学习Python，想开发一个OpenFlow应用程序。我现在做的这个应用是一个简单的以太网交换机，代码在这里：

https://github.com/osrg/ryu/blob/master/ryu/app/simple_switch.py

我还有另一个文件：

https://github.com/osrg/ryu/blob/master/ryu/topology/api.py

这个文件看起来是用来获取拓扑中链接和交换机信息的。

但是如果我在simple_switch.py的init()函数里调用这个文件中的函数，就会出现错误。

   def __init__(self, *args, **kwargs):
        super(SimpleSwitch, self).__init__(*args, **kwargs)
        self.mac_to_port = {}
        s_list = get_all_switch(app_manager)

这是我遇到的错误。

loading app ryu/app/simple_switch.py
loading app ryu.controller.ofp_handler
instantiating app ryu.controller.ofp_handler of OFPHandler
instantiating app ryu/app/simple_switch.py of SimpleSwitch
Traceback (most recent call last):
  File "/usr/local/bin/ryu-manager", line 9, in <module>
    load_entry_point('ryu==3.8', 'console_scripts', 'ryu-manager')()
  File "/usr/local/lib/python2.7/dist-packages/ryu/cmd/manager.py", line 73, in main
    services.extend(app_mgr.instantiate_apps(**contexts))
  File "/usr/local/lib/python2.7/dist-packages/ryu/base/app_manager.py", line 434, in instantiate_apps
    self._instantiate(app_name, cls, *args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/ryu/base/app_manager.py", line 420, in _instantiate
    app = cls(*args, **kwargs)
  File "/home/karthik/Projects/ryu/ryu/app/simple_switch.py", line 35, in __init__
    s_list = get_all_switch(app_manager)
NameError: global name 'get_all_switch' is not defined

我有几个问题：

1) 我能否通过在ryu/topology/api.py中定义的get_all_switch()和get_all_link()来获取我的mininet拓扑信息？

2) 如果可以，为什么上面的代码没有按预期工作？

我在这里问是因为我对Python的了解还不够深入。我想在simple_switch.py中使用topology/api.py里的函数。

在simple_switch.py中的导入部分是这样的：

import logging
import struct

from ryu.base import app_manager
from ryu.controller import mac_to_port
from ryu.controller import ofp_event
from ryu.controller.handler import MAIN_DISPATCHER
from ryu.controller.handler import set_ev_cls
from ryu.ofproto import ofproto_v1_0
from ryu.lib.mac import haddr_to_bin
from ryu.lib.packet import packet
from ryu.lib.packet import ethernet

根据答案1的更新：

我修改了我的代码，如下所示：

from ryu.base import app_manager
from ryu.controller import mac_to_port
from ryu.controller import ofp_event
from ryu.controller.handler import MAIN_DISPATCHER
from ryu.controller.handler import set_ev_cls
from ryu.ofproto import ofproto_v1_0
from ryu.lib.mac import haddr_to_bin
from ryu.lib.packet import packet
from ryu.lib.packet import ethernet
import ryu.topology.api


 def __init__(self, *args, **kwargs):
        super(SimpleSwitch, self).__init__(*args, **kwargs)
        self.mac_to_port = {}
        s_list = ryu.topology.api.get_all_switch(app_manager.RyuApp)

现在我遇到了一个新的错误：

loading app ryu/app/simple_switch.py
loading app ryu.topology.switches
loading app ryu.controller.ofp_handler
loading app ryu.controller.ofp_handler
instantiating app ryu.topology.switches of Switches
instantiating app ryu.controller.ofp_handler of OFPHandler
instantiating app ryu/app/simple_switch.py of SimpleSwitch
Traceback (most recent call last):
  File "/usr/local/bin/ryu-manager", line 9, in <module>
    load_entry_point('ryu==3.8', 'console_scripts', 'ryu-manager')()
  File "/usr/local/lib/python2.7/dist-packages/ryu/cmd/manager.py", line 73, in main
    services.extend(app_mgr.instantiate_apps(**contexts))
  File "/usr/local/lib/python2.7/dist-packages/ryu/base/app_manager.py", line 434, in instantiate_apps
    self._instantiate(app_name, cls, *args, **kwargs)
  File "/usr/local/lib/python2.7/dist-packages/ryu/base/app_manager.py", line 420, in _instantiate
    app = cls(*args, **kwargs)
  File "/home/karthik/Projects/ryu/ryu/app/simple_switch.py", line 36, in __init__
    s_list = ryu.topology.api.get_all_switch(app_manager.RyuApp)
  File "/usr/local/lib/python2.7/dist-packages/ryu/topology/api.py", line 26, in get_all_switch
    return get_switch(app)
  File "/usr/local/lib/python2.7/dist-packages/ryu/topology/api.py", line 21, in get_switch
    rep = app.send_request(event.EventSwitchRequest(dpid))
TypeError: unbound method send_request() must be called with RyuApp instance as first argument (got EventSwitchRequest instance instead)

Answer 1

试着用这一行代码替代：

s_list = ryu.topology.api.get_all_switch(self)

Answer 2

根据上面的回答和一些深入研究，我的代码如下，现在运行得很好：

from ryu.base import app_manager
from ryu.controller import ofp_event
from ryu.controller.handler import CONFIG_DISPATCHER, MAIN_DISPATCHER
from ryu.controller.handler import set_ev_cls
from ryu.ofproto import ofproto_v1_3
from ryu.lib.packet import packet
from ryu.lib.packet import ethernet

from ryu.topology import event
from ryu.topology.api import get_all_switch, get_all_link


class SimpleSwitch13(app_manager.RyuApp):
    OFP_VERSIONS = [ofproto_v1_3.OFP_VERSION]

    def __init__(self, *args, **kwargs):
        super(SimpleSwitch13, self).__init__(*args, **kwargs)
        self.mac_to_port = {}

    @set_ev_cls(ofp_event.EventOFPSwitchFeatures, CONFIG_DISPATCHER)
    def switch_features_handler(self, ev):
        self.logger.info("Received EventOFPSwitchFeatures")
        msg = ev.msg
        self.logger.info('OFPSwitchFeatures received: '
                         '\n\tdatapath_id=0x%016x n_buffers=%d '
                         '\n\tn_tables=%d auxiliary_id=%d '
                         '\n\tcapabilities=0x%08x',
                         msg.datapath_id, msg.n_buffers, msg.n_tables,
                         msg.auxiliary_id, msg.capabilities)

        datapath = ev.msg.datapath
        ofproto = datapath.ofproto
        parser = datapath.ofproto_parser
        match = parser.OFPMatch()
        actions = [parser.OFPActionOutput(ofproto.OFPP_CONTROLLER,
                                          ofproto.OFPCML_NO_BUFFER)]
        self.add_flow(datapath, 0, match, actions)

    def add_flow(self, datapath, priority, match, actions, buffer_id=None):
        ofproto = datapath.ofproto
        parser = datapath.ofproto_parser

        inst = [parser.OFPInstructionActions(ofproto.OFPIT_APPLY_ACTIONS,
                                             actions)]
        if buffer_id:
            mod = parser.OFPFlowMod(datapath=datapath, buffer_id=buffer_id,
                                    priority=priority, match=match,
                                    instructions=inst)
        else:
            mod = parser.OFPFlowMod(datapath=datapath, priority=priority,
                                    match=match, instructions=inst)
        datapath.send_msg(mod)

    @set_ev_cls(ofp_event.EventOFPPacketIn, MAIN_DISPATCHER)
    def _packet_in_handler(self, ev):
        #self.logger.info("Received EventOFPPacketIn")
        # If you hit this you might want to increase
        # the "miss_send_length" of your switch
        if ev.msg.msg_len < ev.msg.total_len:
            self.logger.debug("packet truncated: only %s of %s bytes",
                              ev.msg.msg_len, ev.msg.total_len)
        msg = ev.msg
        datapath = msg.datapath
        ofproto = datapath.ofproto
        parser = datapath.ofproto_parser
        in_port = msg.match['in_port']

        pkt = packet.Packet(msg.data)
        eth = pkt.get_protocols(ethernet.ethernet)[0]

        dst = eth.dst
        src = eth.src

        dpid = datapath.id
        self.mac_to_port.setdefault(dpid, {})

        self.logger.info("\tpacket in %s %s %s %s", dpid, src, dst, in_port)

        # learn a mac address to avoid FLOOD next time.
        self.mac_to_port[dpid][src] = in_port

        if dst in self.mac_to_port[dpid]:
            out_port = self.mac_to_port[dpid][dst]
        else:
            out_port = ofproto.OFPP_FLOOD

        actions = [parser.OFPActionOutput(out_port)]

        # install a flow to avoid packet_in next time
        if out_port != ofproto.OFPP_FLOOD:
            match = parser.OFPMatch(in_port=in_port, eth_dst=dst)
            # verify if we have a valid buffer_id, if yes avoid to send both
            # flow_mod & packet_out
            if msg.buffer_id != ofproto.OFP_NO_BUFFER:
                self.add_flow(datapath, 1, match, actions, msg.buffer_id)
                return
            else:
                self.add_flow(datapath, 1, match, actions)
        data = None
        if msg.buffer_id == ofproto.OFP_NO_BUFFER:
            data = msg.data

        out = parser.OFPPacketOut(datapath=datapath, buffer_id=msg.buffer_id,
                                  in_port=in_port, actions=actions, data=data)
        datapath.send_msg(out)

    """
    The event EventSwitchEnter will trigger the activation of get_topology_data().
    """
    @set_ev_cls(event.EventSwitchEnter, [MAIN_DISPATCHER,CONFIG_DISPATCHER])
    def get_topology_data(self, ev):
        self.logger.info("[Ehsan] Received EventSwitchEnter")
        # Call get_switch() to get the list of objects Switch.
        switch_list = get_all_switch(self)

        # Build a list with all the switches ([switches])
        topo_switches = [switch.dp.id for switch in switch_list]

        # Call get_link() to get the list of objects Link.
        links_list = get_all_link(self)

        # Build a  list with all the links [(srcNode, dstNode, port)].
        topo_links = [(link.src.dpid,link.dst.dpid,{'port':link.src.port_no}) for link in links_list]

        print ("\tLinks: "+str(topo_links))
        print ("\tSwitches: "+str(topo_switches))

目前，我的这个功能是在连接开关时触发的，但你可以修改 get_topology_data() 这个函数，让它在任何事件发生时都能调用。比如，当接收到端口状态时，或者链接被删除、添加或修改时，你都可以调用它来更新拓扑结构。

请注意，我现在还在开发这个代码的阶段。以后我可能会把完整的代码放到我的 代码库 上。

Answer 3

1. 是的。
2. 很可能你应该使用一个带有前缀的名称，比如 ryu.topology.api.get_all_switch()。要给出更准确的答案，需要更多的上下文信息（比如，展示一下你的 import 语句）。