# coding=utf8

refs = []

f = open('C:\\Users\\lx201\\Desktop\\11.txt', encoding='utf8')

for line in f:
        refs.append(line)

        refs.sort(key=lambda x:(x[0], x[1]))

count = 0
for i in refs:
      count +=1
    print('[' + str(count) + ']' + ' ' + i, end='')

  原有的参考文献存在11.txt中，结果会print出来。