Once PEP 3137 is fully implemented, the re module needs to be fixed so
that the regex argument, the substitution argument, and the argument
being searched/replaced are allowed to be arbitrary bytes arrays; where
hashing is needed a copy in an immutable bytes object can be made.

re has supported bytes for a while now.

Actually non-hashable patterns are not supported.

>>> re.match(bytearray(b'.'), b'x')
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
  File "/home/serhiy/py/cpython/Lib/re.py", line 163, in match
    return _compile(pattern, flags).match(string)
  File "/home/serhiy/py/cpython/Lib/re.py", line 281, in _compile
    p, loc = _cache[type(pattern), pattern, flags]
TypeError: unhashable type: 'bytearray'

Should it be considered as a bug?

Hm, I don't see a reason why the *pattern* should be a bytearray or memoryview, only the string it is searching. But if you fixed it by casting it to bytes I won't stop you. :-)

It is easy to fix with small (but non zero) cost, but I don't see a reason too. 
So I don't reopen this issue.