>>> "hello world".decode("utf-8")
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    AttributeError: 'str' object has no attribute 'decode'
    >>> b"hello world".encode("utf-8")
    Traceback (most recent call last):
      File "<stdin>", line 1, in <module>
    AttributeError: 'bytes' object has no attribute 'encode'