Pyusb: Why Are Bus.dirname And Dev.filename Empty String?

I am very new to using PyUSB. I have some USB devices connected to my machine and am trying to get some of their properties. Based on what I have learnt from other examples using

Solution 1:

The device number is in devnum:

busses = usb.busses()
   for bus in busses:
       devices = bus.devices
       for dev in devices:
          print dev.devnum #filename is empty!!
          print bus.dirname
          print dev.idProduct