\l operation in regular expressions

[Kalle Anka]

I've started to play around with regexps in Python and I tried
something like this

print re.sub( r'(\bw\w+\b)', r'\u\1', 'will it work')

and get

\uwill it \uwork

when I had expected

Will it Work

I tried to find some documentation about this but I can't find anything
that says if operations like \l \L \u \U etc are supported or not. It
doesn't look like it supported? What is the "Python way" of doing this,
writing a function and use that as the replacement?