[Python-3000] Weird error message from bytes type

[Neil Schemenauer]

>>> x = b'a'
>>> x[0] = b'a'
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
TypeError: 'bytes' object cannot be interpreted as an index

Huh?  0 is not a 'bytes' object and I don't see how the RHS is being
used as an index.  Obviously I wanted something like:

>>> x[0] = ord(b'a')