【python】列表里包含字典，怎么嵌套循环？

lis = [{"A":"a1","B":"b1"},{"A":"a2","B":"b2"}]
怎么循环，最终生成[a1,b1,a2,b2]
请赐教，非常感谢。

lis = [{"A":"a1","B":"b1"},{"A":"a2","B":"b2"}]

res = []

for i in lis:
    res.extend(i.values())
print(res)

lis = [{"A":"a1","B":"b1"},{"A":"a2","B":"b2"}]
a = []
for i in lis:
    for key, value in i.items():
        a.append(value)
print(a)