Correct handling of case in unicode and regexps

[Devin Jeanpierre]

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