Python上下文管理的成员变量？

上下文管理器定义设置/清理功能__enter__ and __exit__。惊人的。我想保留一个作为成员变量。当我的类对象超出范围时，我希望执行此清理操作。据我所知，这基本上是 C++ 构造函数/析构函数自动发生的行为。

class Animal(object):

    def __init__(self): 
        self.datafile = open("file.txt") # This has a cleanup function
        # I wish I could say something like...
        with open("file.txt") as self.datafile: # uh...

    def makeSound(self):
        sound = self.datafile # I'll be using it later

# Usage...
if True:
    animal = Animal()
# file should be cleaned up and closed at this point.

我给班级一个close函数如果有意义，然后使用closing上下文管理器：

class MyClass(object):
    def __init__(self):
        self.resource = acquire_resource()

    def close():
        release_resource(self.resource)

然后像这样使用它：

from contextlib import closing

with closing(MyClass()) as my_object:
    # use my_object