+
−str_range = '4-7, 9, 12, 15'
+
−
+
−ranges = str_range.split(',')
+
−
+
−lst = []
+
−for r in ranges:
+
−    vals = r.split('-')
+
−    if len(vals) == 2:
+
−       lst.extend(range(int(vals[0]), int(vals[1]) + 1))
+
−    else:
+
−       lst.append(int(vals[0]))
+
−
+
−set_range = set(lst)
+
−all_elems = set(range(min(lst), max(lst)))
+
−
+
−print all_elems - set_range