When starting the script something went wrong:

./mqtt2rrd.py -v

Traceback (most recent call last):
File "./mqtt2rrd.py", line 113, in
client.loop_forever()
File "/usr/lib/python3/dist-packages/paho/mqtt/client.py", line 1481, in loop_forever
rc = self.loop(timeout, max_packets)
File "/usr/lib/python3/dist-packages/paho/mqtt/client.py", line 1003, in loop
rc = self.loop_read(max_packets)
File "/usr/lib/python3/dist-packages/paho/mqtt/client.py", line 1284, in loop_read
rc = self._packet_read()
File "/usr/lib/python3/dist-packages/paho/mqtt/client.py", line 1849, in _packet_read
rc = self._packet_handle()
File "/usr/lib/python3/dist-packages/paho/mqtt/client.py", line 2311, in _packet_handle
return self._handle_connack()
File "/usr/lib/python3/dist-packages/paho/mqtt/client.py", line 2372, in _handle_connack
self.on_connect(self, self._userdata, flags_dict, result)
TypeError: on_connect() takes 3 positional arguments but 4 were given

I'm using Ubuntu 18.04.
What's wrong?

Best regards,
Guenther