Failure in writing binary text to file

[Gribouillis]

If you encode an ascii string with the UTF-8 encoding, it does not change a single byte. For non ascii characters there are more bytes.

>>> "Hello InfinityQuest!".encode('utf-8')
b'Hello InfinityQuest!'
>>> "hétérogénéité".encode('utf-8')
b'h\xc3\xa9t\xc3\xa9rog\xc3\xa9n\xc3\xa9it\xc3\xa9'

Your way to write binary files is perfect.