unicodedata implementation - categories

[James Abley]

Hi,

I'm trying to understand how CPython implements unicodedata, with a view to
providing an implementation for Jython. This is a background, low priority
thing for me, since I last posted to this list about it in February!

Python 2.5.1 (r251:54863, May  2 2007, 16:56:35)
[GCC 4.1.2 (Ubuntu 4.1.2-0ubuntu4)] on linux2
Type "help", "copyright", "credits" or "license" for more information.
>>> import unicodedata
>>> c = unichr(0x10FFFF)
>>> unicodedata.name(c)
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
ValueError: no such name
>>> unicodedata.category(unichr(0x10FFFF))
'Cn'

0x10FFFF is not a valid codepoint in Unicode 4.1, which is the version of
the Unicode standard that Python 2.5 supports.

So I have a couple of questions:

1) Why doesn't the category method raise an Exception, like the name method
does?
2) Given that the category method doesn't currently raise an Exception,
please could someone explain how the category is calculated? I have tried to
figure it out based on the CPython code, but I have thus far failed, and I
would also prefer to have it explicitly defined, rather than mandating that
a Jython (.NET, etc) implementation uses the same (possibly non-optimal for
Java) data structures and algorithms. 

My background is Mathematics rather than pure Computer Science, so doubtless
I still have some gaps in my education to be filled when it comes to data
structures and algorithms and I would welcome the opportunity to fill some
of those in. References to Knuth or some on-line reading would be much
appreciated, to help me understand the CPython part.

Cheers,

James
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