如何使python类成为上下文管理器

我这样定义我的类：

class Simple():
    def __init__(self):
        self.string = "Hello World"

    def __enter__(self):
        pass

    def __exit__(self):
        pass

with Simple() as simple_test:
    print(simple_test.string)

这样称呼它：

class Simple():
    def __init__(self):
        self.string = "Hello World"

    def __enter__(self):
        pass

    def __exit__(self):
        pass

with Simple() as simple_test:
    print(simple_test.string)

我得到以下错误：

    print(simple_test.string)
AttributeError: 'NoneType' object has no attribute 'string'

---

为什么我的类

None

？

方法必须返回

self

：

def __enter__(self):
    return self

---

\uuuu enter\uuuu

应在

as

子句中返回要绑定的内容，请参阅

因为您的

\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu

我想你想要这个：

class Simple():
    def __init__(self):
        self.string = "Hello World"

    def __enter__(self):
        return self

    def __exit__(self):
        pass

simple\u test
被分配了
\uuuuuuuuuuuuuuuuuuuuuuuuu
方法的返回值-你需要从
\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu>方法返回
。我今天花了几个小时在这个问题上，没有规范？
\uuuu退出\uuuu
方法只应执行清理。它不会返回任何东西…我（最终意识到）的理解是它应该是
\uuuuuuu退出（self，exc\u type，exc\u value，exc\u traceback）
？是的，如果你想在
\uuuu退出
中使用它，你可以。如果您只想
传递
它，并且添加了
\uuuuuuuuuuuuuuuuuuuuuuuuuuuuu
它只是为了实现上下文管理器，那么您可以将
\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu
函数不带参数（仅限self），顺便说一句，如果它对您有帮助，请接受答案，以便帮助其他正在处理类似问题。