__getitem__，__setitem__，__delitem__

用于索引操作，如字典。以上分别表示获取，设置，删除数据

class Foo(object):
    def __getitem__(self, key):
        print('__getitem__',key)

    def __setitem__(self, key, value):
        print('__setitem__',key,value)

    def __delitem__(self, key):
        print('__delitem',key)

obj = Foo()
# 自动触发执行__getitem__
result = obj['k1']      # __getitem__ k1
# 自动触发执行__setitem__
obj['k2'] = 'laowang'   # __setitem__ k2 laowang
# 自动触发执行__delitem__
del obj['k1']           # __delitem k1