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

James Y Knight foom at fuhm.net
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.


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