Yeah, now it works.
The script looks like this:
Code
import sys
sys.path.append('/storage/.kodi/addons/service.mqtt/lib')
import client as mqtt
broker_address="192.168.XXX.XXX"
client = mqtt.Client("P1") #create new instance
client.connect(broker_address) #connect to broker
client.publish("cmnd/bruecke1/power","ON")#publish
Now when the script is started this way
"python test.py"
a payload named "ON" is published to the topic "cmnd/bruecke1/power".
Thanks for your help.
Maybe this can help someone else...
Greetings
Yankee