`open` also defaults to your system encoding, which is likely utf8 judging from the message.
print(str(b'I DONT WANT TO add "UTF-8" everywhere!!','UTF-8'))
not quite default!
The encode (or is it decode? I always forget) defaults to utf8, which is what you should be using.
print('I DONT WANT TO add "UTF-8" everywhere!!')
And get the same result. Or if you really want to start with bytes:
print(b'some string'.decode())
`open` also defaults to your system encoding, which is likely utf8 judging from the message.