How to interpret a device’s USB location (i.e. 1-3.2.1)

I have a script that needs to unbind/bind a device and to do that, I need to retrieve the USB location. When I enumerate the ports using pyserial, I get the following:

ttyACM3 Numato 1-3.2.1:1.1 

But when I do the unbind/bind, I believe what I want to use is just this portion of it:

1-3.2.1

That got me wondering what the “:1.1” was, so I went to /sys/bus/usb/devices and I noticed that I have the following:

lrwxrwxrwx 1 root root 0 Sep  3 12:53 1-3.2.1 -> ../../../devices/pci0000:00/0000:00:14.0/usb1/1-3/1-3.2/1-3.2.1/ lrwxrwxrwx 1 root root 0 Sep  3 12:53 1-3.2.1:1.0 -> ../../../devices/pci0000:00/0000:00:14.0/usb1/1-3/1-3.2/1-3.2.1/1-3.2.1:1.0/ lrwxrwxrwx 1 root root 0 Sep  3 12:53 1-3.2.1:1.1 -> ../../../devices/pci0000:00/0000:00:14.0/usb1/1-3/1-3.2/1-3.2.1/1-3.2.1:1.1/ lrwxrwxrwx 1 root root 0 Sep  3 12:53 1-3.2.1:1.2 -> ../../../devices/pci0000:00/0000:00:14.0/usb1/1-3/1-3.2/1-3.2.1/1-3.2.1:1.2/ lrwxrwxrwx 1 root root 0 Sep  3 12:53 1-3.2.1:1.3 -> ../../../devices/pci0000:00/0000:00:14.0/usb1/1-3/1-3.2/1-3.2.1/1-3.2.1:1.3/ 

I know the beginning of the location has to do with the hierarchy of the USB bus and the hubs, etc – what is the stuff after the colon (1.0, 1.1, 1.2, and 1.3)? It seems like /sys/bus/usb/devices/1-3.2.1 contains all the main details for the device, but I was curious what all the other folders are.

The other reason I ask is because when I use pyserial to list all the devices and their USB locations, is it safe to just truncate everything after the colon when I want the device location?