numberedstrings.py

import re
import itertools

key_re = re.compile(r'(.*?)(\d*)$')

def string_key(s):
    name, number = key_re.match(s).groups()
    return (name, number and int(number))

def group_key((i, (name, number))):
    if number != '':
        return i - number
    return name

def group_numbered_strings(strings, format_str='%s-%s'):
    indexed_keys = enumerate(itertools.imap(string_key, strings))
    for key, group in itertools.groupby(indexed_keys, group_key):
        group = list(group)
        first_string = '%s%s' % group[0][1]
        if len(group) > 1:
            last_string = '%s%s' % group[-1][1]
            yield format_str % (first_string, last_string)
        else:
            yield first_string