list_sort

class Info:
        def __init__(self, index, name):
                self.name = name
                self.index = index
        def __repr__(self):
                return repr((self.name, self.index))

inf1 = Info(2, "two")
inf2 = Info(1, "one")
inf3 = Info(-1, "Minus-one")
inf4 = Info(3, "Three")
inf5 = Info(0, "Zero")

list_of_info = [inf1, inf2, inf3, inf4, inf5]

list_sorted =  sorted(list_of_info, key=lambda info: info.index)
print list_sorted
def validate(list_obj):
  flag = 0
  prev = list_obj[0].index
  for info in list_sorted[1:]:
    if info.index - prev != 1 and info.index - prev != -1:
      print 'invalid sequence'
    return
    if info.index == 0:
      flag = 1
    prev = info.index

  print 'sequence is correct'
  print list_obj

validate(list_sorted)