1 str_range = '4-7, 9, 12, 15'

     2 

     3 ranges = str_range.split(',')

     4 

     5 lst = []

     6 for r in ranges:

     7     vals = r.split('-')

     8     if len(vals) == 2:

     9        lst.extend(range(int(vals[0]), int(vals[1]) + 1))

    10     else:

    11        lst.append(int(vals[0]))

    12 

    13 set_range = set(lst)

    14 all_elems = set(range(min(lst), max(lst)))

    15 

    16 print all_elems - set_range