Python使用Paho MQTT出现ConnectionError未定义错误求助

我用以下代码通过WebSocket+SSL连接带密码验证的MQTT broker：

import paho.mqtt.client as mqtt
import ssl
import time

def on_connect(client, userdata, flags, rc):
    print("connected with result code "+str(rc))

def on_publish(client, userdata, mid):
    print("mid: "+str(mid))

client = mqtt.Client('device', transport="websockets")
client.on_connect = on_connect
client.on_publish = on_publish

client.username_pw_set("login", "pass")
client.ws_set_options(path="/logger")
client.tls_set(ca_certs=None, certfile=None, keyfile=None, cert_reqs=ssl.CERT_REQUIRED,
    tls_version=ssl.PROTOCOL_TLS, ciphers=None)

connection = False


print("Trying to connect ...")
client.connect(host="mqtt.broker.io", port=443)
connection = True

for _ in range(5):
    time.sleep(1)
    client.publish("some/topic", "HELLO", qos=2)
    client.loop(1)

client.disconnect()

运行时抛出以下错误：

Trying to connect ... connected with result code 0 Traceback (most
recent call last): File
"/home/souvik/GitLab/Embedded/demo_mqtt_auth.py", line 30, in
client.loop(1) File "/home/souvik/.local/lib/python2.7/site-packages/paho/mqtt/client.py",
line 1120, in loop
return self._loop(timeout) File "/home/souvik/.local/lib/python2.7/site-packages/paho/mqtt/client.py",
line 1164, in _loop
rc = self.loop_read() File "/home/souvik/.local/lib/python2.7/site-packages/paho/mqtt/client.py",
line 1556, in loop_read
rc = self._packet_read() File "/home/souvik/.local/lib/python2.7/site-packages/paho/mqtt/client.py",
line 2373, in _packet_read
except ConnectionError as err: NameError: global name 'ConnectionError' is not defined

sleepiz_one on  hw-1929-diagnostics [$!] on  (eu-west-1) took 6s ❯
/bin/python /home/souvik/GitLab/Embedded/demo_mqtt_auth.py Trying to
connect ... connected with result code 0 Traceback (most recent call
last): File "/home/souvik/GitLab/Embedded/demo_mqtt_auth.py", line
30, in
client.loop(1) File "/home/souvik/.local/lib/python2.7/site-packages/paho/mqtt/client.py",
line 1120, in loop
return self._loop(timeout) File "/home/souvik/.local/lib/python2.7/site-packages/paho/mqtt/client.py",
line 1164, in _loop
rc = self.loop_read() File "/home/souvik/.local/lib/python2.7/site-packages/paho/mqtt/client.py",
line 1556, in loop_read
rc = self._packet_read() File "/home/souvik/.local/lib/python2.7/site-packages/paho/mqtt/client.py",
line 2373, in _packet_read
except ConnectionError as err: NameError: global name 'ConnectionError' is not defined

虽然抛出异常，但数据已经成功发送到broker。补充信息：使用paho-mqtt 1.6.1版本，Python版本为2.7。

这个错误的核心原因是Python 2.7没有ConnectionError这个内置异常类，它是Python 3.3及以上版本才新增的。而你用的paho-mqtt 1.6.1源码里直接引用了这个Python 2.7不存在的异常，所以触发了NameError。

有两种可行的解决方式：

1. 升级Python版本：直接切换到Python 3.3+，从根源上解决兼容性问题，这也是长期来看最稳妥的方案。
2. 修改paho-mqtt源码：如果必须保留Python 2.7，找到本地安装的paho-mqtt包中的client.py文件（路径为/home/souvik/.local/lib/python2.7/site-packages/paho/mqtt/client.py），定位到第2373行的except ConnectionError as err:，替换为Python 2.7兼容的异常捕获逻辑：

   except (IOError, OSError) as err:
   

   因为Python 2.7中，网络连接相关错误会抛出IOError或OSError，替换后就能正常捕获异常，不会再触发NameError。

另外，你的代码可以优化一下消息循环的写法，用loop_start()启动后台循环，避免每次publish后手动调用loop(1)，代码会更简洁稳定：

print("Trying to connect ...")
client.connect(host="mqtt.broker.io", port=443)
client.loop_start()  # 启动后台消息循环

for _ in range(5):
    time.sleep(1)
    client.publish("some/topic", "HELLO", qos=2)

time.sleep(2)  # 等待QoS2消息的确认流程完成
client.loop_stop()
client.disconnect()

内容的提问来源于stack exchange，提问作者Souvik Saha