Installing the paho-mqtt package

I am not an expert on packaging, corrections and clarifications welcome!

Outside any virtual environment

Performing pip install paho-mqtt or any of its variants, pip3, python3 -m pip, etc. performs a 'local install'. If WeeWX was installed via the OS package manager, sudo is required to install MQTTSubscribe. When sudo is used, the local installation of paho-mqtt will not be found.

One way to get around this is to use sudo pip install paho-mqtt. This is discouraged because installing python packages this way may break system dependencies.

The preferred way appears to be, installing paho-mqtt with the OS package manager. The package python3-paho-mqtt seems to be widely available. So for exampke on debian flavors of linux it would be sudo apt install python3-paho-mqtt.

Using a virtual environment

Because you are in a virtual environment, pip install paho-mqtt installs into that environment and the OS is protected.