De-pack string representation of page ranges into an int list, sort, and re-pack

gistfile1.py

def depack(value):
    """

    :type value: str
    """
    print "depack"
    page_list = []
    for part in value.split(','):
        if '-' in part:
            a, b = part.split('-')
            a, b = int(a), int(b)
            page_list.extend(range(a, b + 1))
        else:
            a = int(part)
            page_list.append(a)
    return page_list

def repack(page_list):
    """
    Returns a string representation from integers in a list

    :type value: list
    """
    print "repack"
    # Need to sort the list first
    sorted_values = sorted(page_list, key=int)

    ranges = []
    for key, group in groupby(enumerate(sorted_values), lambda (index, item): index - item):
        group = map(itemgetter(1), group)
        if len(group) > 1:
           ranges.append(xrange(group[0], group[-1])) # under 3.x, switch to "range"
        else:
            ranges.append(group[0])

    ranges_strings = []
    for item in ranges:
        if isinstance(item, xrange): # This only works under Python 2.x - under 3.x, switch to "range"
            # 1-2
            range = "%d-%d" % (item[0], item[-1]+1)
            ranges_strings.append(range)
        else:
            ranges_strings.append(str(item))

    return ", ".join([unicode(s) for s in ranges_strings])