Python合并多个字典

有两个字典，形如

a = {"key": "a@qq.com"}
b = {"key": "b@163.com"}

如何根据相同的key将a，b合并成一个字典？如：

c = {"key": "a@qq.com,b@qq.com"}
或者
c = {"key": "[a@qq.com, b@qq.com]"}

---

from collections import defaultdict
d = defaultdict(list)

d['key'].append(value1)   #value1 = d1['key']
d['key'].append(value2)

---

{ k:[a[k],b[k]] for k in a }

---

不知道下面的代码符不符合你的要求

dic1={"name":"paul","age":25};
dic2={"name":"mark","age":23};

dic={};

for key in dic1:
    if dic2[key] is not None:
        dic[key]=str(dic1[key])+","+str(dic2[key]);
    else:
        dic[key]=dic1[key];

for key in dic2:
    if dic[key] is None:
        dic[key]=dic2[key];

print(str(dic))