Python Barcode and NFC reader using evdev and asyncio

main.py

#!/usr/bin/env python3

import asyncio
from evdev import InputDevice, categorize, ecodes


INPUT_NFC = "/dev/input/by-id/usb-Sycreader_RFID_Technology_Co.__Ltd_SYC_ID_IC_USB_Reader_08FF20140315-event-kbd"
INPUT_BARCODE = "/dev/input/by-id/usb-USB_Adapter_USB_Device-event-kbd"

DEV_NFC = InputDevice(INPUT_NFC)
DEV_BARCODE = InputDevice(INPUT_BARCODE)

SCAN_CODES = { 
    # 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', 57: u' ', 100: u'RALT' 
} 

CAPS_CODES = { 
    0: None, 1: u'ESC', 2: u'!', 3: u'@', 4: u'#', 5: u'$', 6: u'%', 7: u'^', 8: u'&', 9: u'*', 
    10: u'(', 11: u')', 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', 57: u' ', 100: u'RALT' 
}

class DeviceReader:
  """Reads async and calls the callback onLine when enter is pressed.
  You have to replace onLine with your own callback.
  """
  buffer = ""
  caps = False
  onLine = lambda line: None

  def __init__(self, device):
    self.device = device

  async def readDevice(self):
    async for ev in self.device.async_read_loop():
      if ev.type == ecodes.EV_KEY:
        data = categorize(ev)
        
        if data.scancode == ecodes.KEY_LEFTSHIFT:
          self.caps = data.keystate == 1
        
        if data.keystate == 1: # down
          lookup = CAPS_CODES if self.caps else SCAN_CODES
          key = u'{}'.format(lookup.get(data.scancode))
          if (data.scancode != ecodes.KEY_LEFTSHIFT) and (data.scancode != ecodes.KEY_ENTER):
            if key != None:
              self.buffer += key
          elif data.scancode == ecodes.KEY_ENTER:
            if self.onLine:
              line = self.buffer
              self.buffer = ""
              self.onLine(line)

if __name__ == "__main__":
  try:
    DEV_BARCODE.grab()
    DEV_NFC.grab()

    barcode = DeviceReader(DEV_BARCODE)
    nfc = DeviceReader(DEV_NFC)
    
    barcode.onLine = lambda line: print("Barcode scanned: " + line + "\n")
    nfc.onLine = lambda line: print("NFC scanned: " + line + "\n")

    asyncio.ensure_future(barcode.readDevice())
    asyncio.ensure_future(nfc.readDevice())
  
    barcode_loop = asyncio.get_event_loop()
    barcode_loop.run_forever()
  finally:
    DEV_BARCODE.ungrab()
    DEV_NFC.ungrab()

main_nfc.py

#!/usr/bin/env python3

def loadUsers():
  """Reads NFC UUID to User mapping from users.txt
  """
  users = dict()
  with open("users.txt", "r") as f:
    for line in f.readlines():
      if line.startswith("#") or line.strip() == "":
        continue
      parts = line.split(" ")
      user_uuid = parts[0]
      user_name = parts[1]
      users[user_uuid] = user_name
  return users

def doSomething(uuid):
  """Do something with the NFC card uuid
  """
  users = loadUsers()
  if uuid in users:
    user = users[uuid]
    print("Found user " + user)
  else:
    print("No user registered for " + uuid)


def main():
  """Read from NFC "keyboard" and do an action
  """
  running = True
  while running:
    try:
      uuid = input("Enter NFC UUID:")
      doSomething(uuid)
    except KeyboardInterrupt:
      running = False
      exit()
    except Exception as e:
      print("Got error:" + str(e))


if __name__ == "__main__":
  main()

requirements.txt

evdev==1.5.0
# and python 3.9

users.txt

12312312 kristian
01010101 github