py3: make sure we return strings from __str__ and __repr__ On Python 3: >>> class abc: ... def __repr__(self): ... return b'abc' ... >>> abc() Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: __repr__ returned non-string (type bytes) >>> class abc: ... def __str__(self): ... return b'abc' ... >>> str(abc()) Traceback (most recent call last): File "<stdin>", line 1, in <module> TypeError: __str__ returned non-string (type bytes) So the __str__ and __repr__ must return strings.