方法一：

>>> xs = {'a': 4, 'b': 3, 'c': 2, 'd': 1}
>>> sorted(xs.items(), key=lambda item: item[1])
[('d', 1), ('c', 2), ('b', 3), ('a', 4)]

方法二：

>>> xs = {'a': 4, 'b': 3, 'c': 2, 'd': 1}
>>> import operator
>>> sorted(xs.items(), key=operator.itemgetter(1))
[('d', 1), ('c', 2), ('b', 3), ('a', 4)]