Search HID devices by name and listen keyboard events

hid.py

# Get event id and names for connected HID devices:
# cat /proc/bus/input/devices  | grep -P '^[NH]: ' | paste - -
#
# To allow current user to run this script without root:
# sudo usermod -a -G input $USER
import evdev
from evdev import InputDevice, categorize  # import * is evil :)
import time
import traceback
import sys

# Provided as an example taken from my own keyboard attached to a Centos 6 box:
scancodes = {
    # Scancode: ASCIICode
    0: None, 1: u'ESC', 2: u'1', 3: u'2', 4: u'3', 5: u'4', 6: u'5', 7: u'6', 8: u'7', 9: u'8',
    10: u'9', 11: u'0', 12: u'-', 13: u'=', 14: u'BKSP', 15: u'TAB', 16: u'Q', 17: u'W', 18: u'E', 19: u'R',
    20: u'T', 21: u'Y', 22: u'U', 23: u'I', 24: u'O', 25: u'P', 26: u'[', 27: u']', 28: u'CRLF', 29: u'LCTRL',
    30: u'A', 31: u'S', 32: u'D', 33: u'F', 34: u'G', 35: u'H', 36: u'J', 37: u'K', 38: u'L', 39: u';',
    40: u'"', 41: u'`', 42: u'LSHFT', 43: u'\\', 44: u'Z', 45: u'X', 46: u'C', 47: u'V', 48: u'B', 49: u'N',
    50: u'M', 51: u',', 52: u'.', 53: u'/', 54: u'RSHFT', 56: u'LALT', 100: u'RALT'
}

class KeyboardReader():
    def __init__(self, keyword, handler=None):
        self.keyword = keyword
        self.devices = self.search_devices()
        # device /dev/input/event21, name "Logitech K400 Plus", phys "usb-0000:00:14.0-2/input2:1"
        self.handler=handler

    def handle_line(self, dev, line):
        print(f'Received line: {line} from {dev.phys}')
        if self.handler is not None:
            self.handler(dev, line)

    def search_devices(self):
        devs = []
        while len(devs) < 1:
            for p in evdev.list_devices():
                dev = InputDevice(p)
                if self.keyword in dev.name:
                    devs.append(dev)
            if len(devs) < 1:
                print(f'Searching for devices {self.keyword}')
                time.sleep(1)
        print(f'Found devices: {devs}')
        return devs

    def listen_device_loop(self, dev):
        keyseq = []
        for event in dev.read_loop():
            if event.type == evdev.ecodes.EV_KEY:
                data = evdev.categorize(event)  # Save the event temporarily to introspect it
                if data.keystate == 1:  # Down events only
                    key = scancodes.get(data.scancode) 
                    if key:
                        if key == u'CRLF':
                            self.handle_line(dev, ''.join(keyseq))
                            keyseq = []
                        else:
                            keyseq.append(key)


    def start(self):
        '''Blocking start handling events
        '''
        for dev in self.devices:
            try:
                self.listen_device_loop(dev)
                # todo read from multiple devices
            except OSError as e:
                traceback.print_exc(file=sys.stdout)
                self.devices = self.search_devices()



if __name__ == '__main__':
    reader = KeyboardReader('Logitech')
    reader.start()