Python 3 异常删除封闭范围内的变量，原因不明

Question

我有以下代码：

def foo():
    e = None
    try:
        raise Exception('I wish you would except me for who I am.')
    except Exception as e:
        print(e)
    print(e)

foo()

在 Python 2.7 中，这按预期运行并打印：

I wish you would except me for who I am.
I wish you would except me for who I am.

然而在Python3.x中，第一行被打印出来，第二行没有。它似乎删除了封闭范围内的变量，从最后一个打印语句中给我以下回溯：

Traceback (most recent call last):
  File "python", line 9, in <module>
  File "python", line 7, in foo
UnboundLocalError: local variable 'e' referenced before assignment

这几乎就像是在 except 块之后插入了一条 del e 语句。这种行为有什么理由吗？如果 Python 开发人员希望 except 块有自己的本地作用域，而不是泄漏到周围的作用域，我可以理解，但是为什么它必须删除先前分配的外部作用域中的变量？

Answer 1

引用 documentation of try,

When an exception has been assigned using as target, it is cleared at the end of the except clause. This is as if
except E as N:
   foo
was translated to
except E as N:
    try:
        foo
    finally:
        del N
This means the exception must be assigned to a different name to be able to refer to it after the except clause. Exceptions are cleared because with the traceback attached to them, they form a reference cycle with the stack frame, keeping all locals in that frame alive until the next garbage collection occurs.

这两个 PEP 中都有介绍。

Python 3 异常删除封闭范围内的变量，原因不明

Python 3 exception deletes variable in enclosing scope for unknown reason

python

exception-handling

exception

python-3.x