Mark Dickinson wrote:
On May 24, 1:13 pm, Steven D'Aprano <st...@remove-this-
cybersource.com.au> wrote:
Do unicode.lower() or unicode.upper() ever change the length of the
string?
The Unicode standard allows for case conversions that change length, e.g.
sharp-S in German should convert to SS:
http://unicode.org/faq/casemap_charprop.html#6
but I see that Python doesn't do that:
s = "Paßstraße"
s.upper()
'PAßSTRAßE'
The more I think about this, the more I think that upper/lower/title case
conversions should change length (at least sometimes) and if Python
doesn't do so, that's a bug. Any thoughts?
Digging a bit deeper, it looks like these methods are using the
Simple_{Upper,Lower,Title}case_Mapping functions described at
http://www.unicode.org/Public/5.1.0/ucd/UCD.html fields 12, 13 and 14
of the unicode data; you can see this in the source in Tools/unicode/
makeunicodedata.py, which is the Python code that generates the
database of unicode properties. It contains code like:
if record[12]:
upper = int(record[12], 16)
else:
upper = char
if record[13]:
lower = int(record[13], 16)
else:
lower = char
if record[14]:
title = int(record[14], 16)
... and so on.
I agree that it might be desirable for these operations to product the
multicharacter equivalents. That idea looks like a tough sell,
though: apart from backwards compatibility concerns (which could
probably be worked around somehow), it looks as though it would
require significant effort to implement.
If we were to make such a change, I think we should also cater for
locale-specific case changes (passing the locale to 'upper', 'lower' and
'title').
For example, normally "i".upper() returns "I", but in Turkish
"i".upper() should return "İ" (the uppercase version of lowercase dotted
i is uppercase dotted I).
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