How to trigger Python script on Raspberry Pi from Node-Red

Node-RED supplies an exec node as part of it's core set, which can be used to call external commands, this could be call your python script.

More details of how to use it can be found in the info sidebar when a copy is dragged onto the canvas.

Or you could wrap the script as a web service or just a simple TCP socket, both of which have nodes that can be used to drive them.