如何合并列表中key相同的字典？

现有list：

list1 = [{a: 123}, {a: 456},{b: 789}]

合并成：

list2 = [{a: [123,456]},{b: [789]}]

from collections import defaultdict
lst = [{'a': 123}, {'a': 456},{'b': 789}]

dic = {}
for _ in lst:
    for k, v in _.items():
        dic.setdefault(k, []).append(v)

print [{k:v} for k, v in dic.items()]