嵌套列表迭代输入特定值会报错：ValueError: list.remove(x): x not in list

Question

#这段代码输入以下值会报错，输入其他值都不报错，一直查不出为什么，请大神们帮忙看下，谢谢。

# 5
# Prashant
# 52.22
# Kush
# 52.223
# Kant
# 52.222
# Kanti
# 52.2222
# Harshit
# 52.22222

M = []
for _ in range(int(raw_input())):
   name = raw_input()
   score = float(raw_input())
   L = []
   L.append(name)
   L.append(score)
   M.append(L)
if len(M) < 2:
   print '2 names must be given at least.'
if len(M) > 5:
   print 'The number of names can not exceed 5'
N = []
for x in M:
   for y in M:
       if x[1] > y[1] and x not in N:
           N.append(x)
for sec in N:
   for bigger in N:
       if sec[1] < bigger[1]:
           N.remove(bigger)
       if sec[1] > bigger[1]:
           N.remove(sec)
N.sort()
for result in N:
   print result[0]

Answer 1

L=[]每次循环都会清零啊