Here's the best I've come up with so far:
pat = sre.compile('(x[x/])+')
(longest, startlongest) = max([(fnd.end()-fnd.start(), fnd.start()) for i in range(len(marks))
for fnd in pat.finditer(marks,i)])
It seems to work, but it's not very smart. Given the string '//////xx//', it returns a list whose first seven tuples are all '(2,6)', followed by a single '(2,7)', which gets returned because of max's secondary attention to the second element in the tuple. In other words this code searches from position 0 and finds (2,6), then searches from position 1 and finds (2,6) . . .
Obviously it ought to adjust the second argument to pat.finditer according to what it finds, instead of blindly stepping. (By the way, I can't give 'range' a stepsize of 2 because the "winning" stretch could begin with an odd-numbered character.) That sounds like a job for a generator. But (1) I haven't been able to work out the details (I'm even shakier on generators than I am on regexes!) and (2) that *seems* likely to be less efficient, maybe by a large enough factor that the obnoxiousness of getting the first search-return seven times is something I should just swallow.
What magic am I missing?
Charles Hartman Professor of English, Poet in Residence http://cherry.conncoll.edu/cohar http://villex.blogspot.com
-- http://mail.python.org/mailman/listinfo/python-list
