Hi! You can control file access using OS level permissions. On Windows, use os.chmod() or the pywin32 module to set permissions so only your app’s user can modify it. On Linux/macOS, os.chmod() with restrictive modes (like 0o600) works. Another approach is to store sensitive data in a database or encrypted file this prevents other apps from easily modifying it. Always test permissions carefully!

You're getting that error because ser.write()doesn't accept lists. It only accepts bytes, bytearray or encoded strings. Right now you're building a list of lists, so Python can't convert it into something the serial port can send. You need to turn your values ​​into a single bytes message before sending, either by encoding them as text or by packing them into a binary format if you need to transmit numbers above 256.