Python 将对象的实例声明为'；全球'；在'__初始'；

我正在维护一个用Python编写的应用程序，遇到了如下情况：

class A():

    def __init__(self):
        ...
        global a
        a = self

    ...

>>> o1 = A()
>>> a is o1    # o1 was most recently instantiated
True
>>> o2 = A()
>>> a is o1    # o1 is no longer the most recently instantiated ...
False
>>> a is o2    # ... o2 is
True

有人能详细解释一下这里发生了什么，以及宣布自我为全球的目的是什么吗？

这两行

global a
a = self

使名为

a

的全局变量引用当前调用其

\uuuu init\uuu

方法的任何对象。实际上，应用程序似乎在跟踪最近实例化的

A

的实例。它应该是这样工作的：

class A():

    def __init__(self):
        ...
        global a
        a = self

    ...

>>> o1 = A()
>>> a is o1    # o1 was most recently instantiated
True
>>> o2 = A()
>>> a is o1    # o1 is no longer the most recently instantiated ...
False
>>> a is o2    # ... o2 is
True