AttributeError: Foo instance has no attribute '__getitem__'

一个object是不能像dict那样通过[]访问的，比如下面这段代码会报错：

>>> class Foo():
...     id = 1
... 
>>> 
>>> f = Foo()
>>> f[id]
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: Foo instance has no attribute '__getitem__'

 正确的做法是通过getattr(obj, name)