Python evdev [Error 16] Device or resource busy

Question

I connected 2D barcode scanner with Raspberry Pi 4 Model B and tried to scan few codes. on using evdev library I got the output successfully. But the issue is after 3 continues scans it's throwing me an exception saying "[Error 16] Device or resource busy". I can't able to find the root cause of this issue and tried many troubleshooting methods but nothing seems to work. Can anyone please help me. Here is the code I used.

from evdev import InputDevice, categorize, ecodes
from datetime import datetime
import calendar

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', 57: u' ', 100: u'RALT'
}

capscodes = {
    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 scan_barcode:
    
    def __init__(self,devicePath):
        self.devicePath = devicePath
        
        
    def readBarcode(self):

        dev = InputDevice(self.devicePath)
        dev.grab() # grab provides exclusive access to the device

        x = ''
        caps = False

        for event in dev.read_loop():
            if event.type == ecodes.EV_KEY:
                data = categorize(event)  # Save the event temporarily to introspect it
                if data.scancode == 42:
                    if data.keystate == 1:
                        caps = True
                    if data.keystate == 0:
                        caps = False

                if data.keystate == 1:  # Down events only
                    if caps:
                        key_lookup = u'{}'.format(capscodes.get(data.scancode)) or u'UNKNOWN:[{}]'.format(data.scancode)  # Lookup or return UNKNOWN:XX
                    else:
                        key_lookup = u'{}'.format(scancodes.get(data.scancode)) or u'UNKNOWN:[{}]'.format(data.scancode)  # Lookup or return UNKNOWN:XX


                    if (data.scancode != 42) and (data.scancode != 28):
                        x += key_lookup

                    if(data.scancode == 28):
                        return(x)

scanned_data = scan_barcode('/dev/input/event0')
def scanner_function():
  try:
    value = scanned_data.readBarcode()
    print(f"Scanned value:{str(value)}")
  except Exception as e:
    print(e)
    pass
while True:
  scanner_function()

Even though when I pass the exception It's not letting me to move to other tasks. The entire process stops here.

This is the output:

Scanned value: 4568hidhXGu
Scanned value: 1238fujXjje75
Scanned value: 789665
[Error 16] Device or resource busy
[Error 16] Device or resource busy
[Error 16] Device or resource busy
[Error 16] Device or resource busy
[Error 16] Device or resource busy

Python evdev [Error 16] Device or resource busy

Answers (1)

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