I'm not sure about FF specifically, but 99% of the time you're connecting a microcontroller to a PC you're doing so over a serial port (UART) of some sort. It may be a physical COM port or it may be a USB to serial adapter or even a purely virtual serial port over a USB connection, but the methodology is all the same. Unless you are running a serial terminal on that port (as in, a commandline on your PC served on the given /dev/ttyX interface, not a terminal emulator letting you read/write from the port), the microcontroller can't just run scripts on the PC. Instead, you will want to write a script/program that opens the port and waits for a command to be sent from the microcontroller, then that listener script can execute whatever functionality you require. Note that only one application can have the port active at a time, so if your listener is a separate program from your event handler, you will have to close the port on the listener before running the handler, then reopen the port on the listener once the handler is done so it can start listening for the next event. Better to just make it all one program that is always running on the PC and does both listening for events and handling them so there's only one program that needs access to the serial port.

From the uc side, open a serial connection, send data. On the host side, prepare a place for received data. On the host side, walk through the received data until the thing you’re looking for is found, then execute some action (in your case a python script).