[Python-Dev] PEP 383: Non-decodable Bytes in System Character Interfaces

Tue Apr 28 07:19:22 CEST 2009

On Apr 27, 2009, at 11:35 PM, Martin v. Löwis wrote:
> No. You seem to assume that all bytes < 128 decode successfully 
> always.
> I believe this assumption is wrong, in general:
>> py> "\x1b$B' \x1b(B".decode("iso-2022-jp") #2.x syntax
> Traceback (most recent call last):
> File "<stdin>", line 1, in <module>
> UnicodeDecodeError: 'iso2022_jp' codec can't decode bytes in position
> 3-4: illegal multibyte sequence
>> All bytes are below 128, yet it fails to decode.

Surely nobody uses iso2022 as an LC_CTYPE encoding. That's expressly 
forbidden by POSIX, if I'm not mistaken...and I can't see how it would 
work, considering that it uses all the bytes from 0x20-0x7f, including 
0x2f ("/"), to represent non-ascii characters.
Hopefully it can be assumed that your locale encoding really is a non- 
overlapping superset of ASCII, as is required by POSIX...
I'm a bit scared at the prospect that U+DCAF could turn into "/", that 
just screams security vulnerability to me. So I'd like to propose 
that only 0x80-0xFF <-> U+DC80-U+DCFF should ever be allowed to be 
encoded/decoded via the error handler.
James