The reason for why the whole unicode checking is done in python3 is to guarantee Unicode support in python3. I actually disliked the old half-string-half-binary

The reason for why the whole unicode checking is done in python3 is to guarantee Unicode support in python3. I actually disliked the old half-string-half-binary approach and almost from the start enjoyed the clear distinction between str and bytes in python3. That being said, the strings/bytes cleanup was also one of the few things that really broke backward compatibility with 2.x.