Why can't I use python-mosquitto on the Raspberry Pi?

Question

I'm using a Raspberry Pi with a Debian Wheezy image. I have installed Mosquitto (the broker of MQTT protocol), mosquitto client and python mosquitto to use mosquitto in my Python script, I have run a very simple example to test if all my packages work fine or not

import mosquitto
mqttc = mosquitto.Mosquitto("python_pub")
mqttc.will_set("/event/dropped", "Sorry, I seem to have died.")
mqttc.connect("127.0.0.1", 1883, 60, True)

mqttc.publish("hello/world", "Hello, World!")

For some reason I get the following error though.

Traceback (most recent call last):
File "test_1.py", line 1, in <module>
import mosquitto
File "/usr/lib/pymodules/python2.7/mosquitto.py", line 484, in <module>
_mosquitto_log_init = _libmosq.mosquitto_log_init
File "/usr/lib/python2.7/ctypes/__init__.py", line 378, in __getattr__
func = self.__getitem__(name)
File "/usr/lib/python2.7/ctypes/__init__.py", line 383, in __getitem__
func = self._FuncPtr((name_or_ordinal, self))
AttributeError: /usr/lib/libmosquitto.so.1: undefined symbol: mosquitto_log

Can somebody explain why this isn't working and a possible solution.

Answer 1

I am actually developing a proyect for my university using mosquitto as a broker of MQTT. I recommend you to use paho as the python module to publish and subscribe using MQTT.

The official page:

https://pypi.python.org/pypi/paho-mqtt

Here is a very simple example that subscribes to the broker $SYS topic tree and prints out the resulting messages (taken from https://pypi.python.org/pypi/paho-mqtt):

import paho.mqtt.client as mqtt

# The callback for when the client receives a CONNACK response from the server.
def on_connect(client, userdata, flags, rc):
    print("Connected with result code "+str(rc))

    # Subscribing in on_connect() means that if we lose the connection and
    # reconnect then subscriptions will be renewed.
    client.subscribe("$SYS/#")

# The callback for when a PUBLISH message is received from the server.
def on_message(client, userdata, msg):
    print(msg.topic+" "+str(msg.payload))

client = mqtt.Client()
client.on_connect = on_connect
client.on_message = on_message

client.connect("iot.eclipse.org", 1883, 60)

# Blocking call that processes network traffic, dispatches callbacks and
# handles reconnecting.
# Other loop*() functions are available that give a threaded interface and a
# manual interface.
client.loop_forever()

Answer 2

The Mosquitto Python module has been donated to the Eclipse Paho project. It can be installed using “pip install paho-mqtt” and there is documentation available at https://pypi.python.org/pypi/paho-mqtt

Existing users of the Mosquitto Python module should find it very easy to port their code to the Paho version.

http://mosquitto.org/documentation/python/

Official example from https://eclipse.org/paho/clients/python/:

import paho.mqtt.client as mqtt

# The callback for when the client receives a CONNACK response from the server.
def on_connect(client, userdata, rc):
    print("Connected with result code "+str(rc))
    # Subscribing in on_connect() means that if we lose the connection and
    # reconnect then subscriptions will be renewed.
    client.subscribe("$SYS/#")

# The callback for when a PUBLISH message is received from the server.
def on_message(client, userdata, msg):
    print(msg.topic+" "+str(msg.payload))

client = mqtt.Client()
client.on_connect = on_connect
client.on_message = on_message

client.connect("iot.eclipse.org", 1883, 60)

# Blocking call that processes network traffic, dispatches callbacks and
# handles reconnecting.
# Other loop*() functions are available that give a threaded interface and a
# manual interface.
client.loop_forever()

Have a try!