上面代码并没有收到snmp消息

抱歉，我给出的示例代码可能没有完全满足你的需求。在接收SNMP消息之前，你需要先设置SNMP引擎并定义处理接收到消息的函数。以下是一个更新的示例代码，可以帮助你实现SNMP v1、v2和v3消息的监听：

from pysnmp.entity import engine, config
from pysnmp.entity.rfc3413 import ntfrcv
from pysnmp.proto.api import v2c

def snmp_listener():
    # SNMP v1/v2c community name
    community_name = 'public'

    # SNMP v3 user credentials
    username = 'username'
    auth_key = 'authkey'
    priv_key = 'privkey'

    # Create SNMP engine
    snmp_engine = engine.SnmpEngine()

    # SNMP v1/v2c setup
    config.addV1System(snmp_engine, 'my-area', community_name)
    config.addTargetParams(snmp_engine, 'my-creds', 'my-area', 'noAuthNoPriv', 1)

    # SNMP v3 setup
    config.addV3User(snmp_engine, username,
                     config.usmHMACMD5AuthProtocol, auth_key,
                     config.usmDESPrivProtocol, priv_key)
    config.addTargetParams(snmp_engine, 'my-creds', username, 'authPriv', 1)

    # SNMP trap receiver
    def trap_receiver(snmp_engine):
        ntfrcv.NotificationReceiver(snmp_engine, handle_trap)

        snmp_engine.transportDispatcher.jobStarted(1)

        try:
            snmp_engine.transportDispatcher.runDispatcher()
        except Exception:
            snmp_engine.transportDispatcher.closeDispatcher()
            raise

    # Handle received trap
    def handle_trap(snmp_engine, state_reference, context_engine_id, context_name, var_binds, cb_ctx):
        for var_bind in var_binds:
            oid = var_bind[0]
            value = var_bind[1]
            print(f'Object type: {oid}, value: {value}')

    # Start the listener
    trap_receiver(snmp_engine)

snmp_listener()

这个示例代码会监听SNMP v1、v2和v3的消息，并通过`handle_trap`函数处理接收到的消息。你可以根据实际需求修改代码中的参数和处理逻辑。请确保你的系统上已经安装了pysnmp库，并且根据需要修改SNMP引擎的配置。