Identifying a particular function of a multifunction input device using evdev

Question

I have some Python code that interacts with a wireless USB numeric keypad. I'd like to be able to discover the device by name, but shows up as multiple input devices. In /dev/input/by-id:

# ls -l /dev/input/by-id
total 0
lrwxrwxrwx 1 root root 9 Sep 25 14:30 usb-MOSART_Semi._2.4G_Keyboard_Mouse-event-kbd -> ../event0
lrwxrwxrwx 1 root root 9 Sep 25 14:30 usb-MOSART_Semi._2.4G_Keyboard_Mouse-if01-event-mouse -> ../event1
lrwxrwxrwx 1 root root 9 Sep 25 14:30 usb-MOSART_Semi._2.4G_Keyboard_Mouse-if01-mouse -> ../mouse0

And using the evdev module:

>>> import evdev
>>> devices = [evdev.InputDevice(dev) for dev in evdev.list_devices()]
>>> for device in devices:
...   print(device.fn, device.name)
...
/dev/input/event1 MOSART Semi. 2.4G Keyboard Mouse
/dev/input/event0 MOSART Semi. 2.4G Keyboard Mouse

Obviously the kernel can distinguish the -kbd device from the -mouse device, but how do I make that determination in my code? The solution I've come up with for now takes advantage of the fact that the "keyboard" device includes the KEY_KP... capabilities, so I can do this:

def is_keyboard(device):
    return evdev.ecodes.KEY_KP1 in device.capabilities()[evdev.ecodes.EV_KEY]

...but that seems more of a heuristic than a reliable test. Is there a way to detect, using the evdev module or an alternative, whether or not a given input device is a keyboard or a mouse (or some frankenstein-like combination of the two)?

Answer 1

It seems no way to directly identify if a given input device is a keyboard or a mouse in evdev. But you can use subprocess as an alternative.

import subprocess

process = subprocess.run("ls -l /dev/input/by-id", shell=True, stdout=subprocess.PIPE)
devices = process.stdout.decode().split("\n")[1:-1]

Then you can get a list like:

[
    "lrwxrwxrwx 1 root root 9 Sep 25 14:30 usb-MOSART_Semi._2.4G_Keyboard_Mouse-event-kbd -> ../event0",
    "lrwxrwxrwx 1 root root 9 Sep 25 14:30 usb-MOSART_Semi._2.4G_Keyboard_Mouse-if01-event-mouse -> ../event1",
    "lrwxrwxrwx 1 root root 9 Sep 25 14:30 usb-MOSART_Semi._2.4G_Keyboard_Mouse-if01-mouse -> ../mouse0"
]