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

"Martin v. Löwis" martin at v.loewis.de
Tue Apr 28 22:25:07 CEST 2009

> The UTF-8b representation suffers from the same potential ambiguities as
> the PUA characters... 

Not at all the same ambiguities. Here, again, the two choices:

A. use PUA characters to represent undecodable bytes, in particular for
   UTF-8 (the PEP actually never proposed this to happen).
   This introduces an ambiguity: two different files in the same
   directory may decode to the same string name, if one has the PUA
   character, and the other has a non-decodable byte that gets decoded
   to the same PUA character.

B. use UTF-8b, representing the byte will ill-formed surrogate codes.
   The same ambiguity does *NOT* exist. If a file on disk already
   contains an invalid surrogate code in its file name, then the UTF-8b
   decoder will recognize this as invalid, and decode it byte-for-byte,
   into three surrogate codes. Hence, the file names that are different
   on disk are also different in memory. No ambiguity.


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