[Python-Dev] PEP 383: Non-decodable Bytes in System Character Interfaces
Stephen J. Turnbull
stephen at xemacs.org
Wed Apr 29 15:14:18 CEST 2009
Baptiste Carvello writes:
> By contrast, if the new utf-8b codec would *supercede* the old one,
> \udcxx would always mean raw bytes (at least on UCS-4 builds, where
> surrogates are unused). Thus ambiguity could be avoided.
Unfortunately, that's false. It could have come from a literal string
(similar to the text above ;-), a C extension, or a string slice (on
16-bit builds), and there may be other ways to do it. The only way to
avoid ambiguity is to change the definition of a Python string to be
*valid* Unicode (possibly with Python extensions such as PEP 383 for
internal use only). But Guido has rejected that in the past;
validation is the application's problem, not Python's.
Nor is a UCS-4 build exempt. IIRC Guido specifically envisioned
Python strings being used to build up code point sequences to be
directly output, which means that a UCS-4 string might none-the-less
contain surrogates being added to a string intended to be sent as
UTF-16 output simply by truncating the 32-bit code units to 16 bits.
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