[Python-Dev] UTF-16 code point comparison
Guido van Rossum
Thu, 27 Jul 2000 08:41:25 -0500
> As far as I can tell, cmp() is the *only* unicode function
> that thinks the internal storage is UTF-16.
> Everything else assumes UCS-2.
> And for Python 2.0, it's surely easier to fix cmp() than to
> fix everything else.
Agreed (I think).
> (this is the same problem as 8-bit/unicode comparisions, where
> the current consensus is that it's better to raise an exception
> if it looks like the programmer doesn't know what he was doing,
> rather than pretend it's another encoding).
> To summarize, here's the "character encoding guidelines" for
> Python 2.0:
> In Unicode context, 8-bit strings contain ASCII. Characters
> in the 0x80-0xFF range are invalid. 16-bit strings contain
> UCS-2. Characters in the 0xD800-0xDFFF range are invalid.
> If you want to use any other encoding, use the codecs pro-
> vided by the Unicode subsystem. If you need to use Unicode
> characters that cannot be represented as UCS-2, you cannot
> use Python 2.0's Unicode subsystem.
> Anything else is just a hack.
I wouldn't go so far as raising an exception when a comparison
involves 0xD800-0xDFFF; after all we don't raise an exception when an
ASCII string contains 0x80-0xFF either (except when converting to
The invalidity of 0xD800-0xDFFF means that these aren't valid Unicode
code points; it doesn't mean that we should trap all attempts to use
these values. That ways, apps that need UTF-16 awareness can code it
Why? Because I don't want to proliferate code that explicitly traps
0xD800-0xDFFF throughout the code.
--Guido van Rossum (home page: http://www.pythonlabs.com/~guido/)