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The `rot_13` codec is supposed to work like this, no?
>>> 'qwerty'.encode('utf-8')
b'qwerty'
>>> 'qwerty'.encode('rot_13')
Traceback (most recent call last):
 File "<pyshell#1>", line 1, in <module>
 'qwerty'.encode('rot_13')
TypeError: encoder did not return a bytes object (type=str)
>>> b'qwerty'.decode('utf-8')
'qwerty'
>>> b'qwerty'.decode('rot_13')
Traceback (most recent call last):
 File "<pyshell#2>", line 1, in <module>
 b'qwerty'.decode('rot_13')
 File "C:\Python32\lib\encodings\rot_13.py", line 19, in decode
 return (input.translate(rot13_map), len(input))
AttributeError: 'memoryview' object has no attribute 'translate'

See #7475.

Ram Rachum wrote:
> The `rot_13` codec is supposed to work like this, no?
No it isn't. In Python 3, str.encode() always encodes to bytes and bytes.decode() always decodes to str. IOW, str.encode() encodes text (Unicode) to data (bytes), and bytes.decode() decodes data to text. ROT-13 is not a character encoding, so it cannot be used in this manner.
It's still available in the codecs module, though:
>>> import codecs
>>> codecs.lookup('rot-13').encode('qwerty')
('djregl', 6)
Other text->text and bytes->bytes codecs are also available there.

Then I suggest replacing this error message:
 encoder did not return a bytes object (type=str)
and this one:
 'memoryview' object has no attribute 'translate'
With something like:
 Please use `codecs.lookup('rot-13').encode`

Issue #7475 discusses fixing the error messages, too.