小编Kip*_*ipi的帖子

假设我有这样的课程：

class a(object): 
    pass
class b(a):
    pass
class c(b): 
    pass
class d(c): 
    pass
class e(b):
    pass

我想要一个可以做类似事情的函数：

>>>get_ inheritance_tree(a)
>>>...b
>>>......c
>>>.........d
>>>......e

我正在尝试运行此代码:

class A:
    def __enter__(self):
        print "enter"
    def __exit__(self, *args):
        print "exit"
    def __init__(self, i):
        self.i = i
with A(10) as a:
    print a.i

我收到这个错误:

enter
exit
Traceback (most recent call last):
File ".last_tmp.py", line 9, in <module>
print a.i
AttributeError: 'NoneType' object has no attribute 'i'

我的语法有什么问题？