class A():
    def __init__(self):
        self.name = {"key": "aaa"}

    def __getitem__(self, item):
        return self.name.get(item)

obj = A()
print(obj["key"])

实现迭代
class B():
    def __init__(self, a_list):
        self.a = a_list
        self.other = "hello, world"

    def __getitem__(self, index):
        return self.a[index]

obj = B(["dog","cat","fish"])
for a in obj:
    print(a)