Correct handling of case in unicode and regexps

Vlastimil Brom vlastimil.brom at gmail.com
Sat Feb 23 16:11:36 CET 2013


2013/2/23 Devin Jeanpierre <jeanpierreda at gmail.com>:
> Hi folks,
>
> I'm pretty unsure of myself when it comes to unicode. As I understand
> it, you're generally supposed to compare things in a case insensitive
> manner by case folding, right? So instead of a.lower() == b.lower()
> (the ASCII way), you do a.casefold() == b.casefold()
>
> However, I'm struggling to figure out how regular expressions should
> treat case. Python's re module doesn't "work properly" to my
> understanding, because:
>
>     >>> a = 'ss'
>     >>> b = 'ß'
>     >>> a.casefold() == b.casefold()
>     True
>     >>> re.match(re.escape(a), b, re.UNICODE | re.IGNORECASE)
>     >>> # oh dear!
>
> In addition, it seems improbable that this ever _could_ work. Because
> if it did work like that, then what would the value be of
> re.match('s', 'ß', re.UNICODE | re.IGNORECASE).end() ? 0.5?
>
> I'd really like to hear the thoughts of people more experienced with
> unicode. What is the ideal correct behavior here? Or do I
> misunderstand things?
>
> -- Devin
> --
> http://mail.python.org/mailman/listinfo/python-list

Hi,
you may check the new regex implementation
https://pypi.python.org/pypi/regex
which does support casefolding in case insensitive matches (beyond
many other features and improvements comparing to re)

hth,
  vbr



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