例子

from itertools import groupby

lst = [5, 4, 4, 4, 5, 5, 2, 5]

for n, l in groupby(lst):
	print n, list(l)

得到

5 [5]
4 [4, 4, 4]
5 [5, 5]
2 [2]
5 [5]

如果

for n, l in groupby(sorted(lst)):
	print n, list(l)

得到

2 [2]
4 [4, 4, 4]
5 [5, 5, 5, 5]