初始化变量时收到“UnboundLocalError：赋值前引用的局部变量‘e’”

[社区编辑给出可重现的示例：]

def main():
    e = None
    print(locals())
    while not e:
        try:
            raise Exception
        except Exception as e:
            pass            

main()

produces

~/coding$ python3.3 quiz2.py
{'e': None}
Traceback (most recent call last):
  File "quiz2.py", line 11, in <module>
    main()
  File "quiz2.py", line 5, in main
    while not e:
UnboundLocalError: local variable 'e' referenced before assignment

[编辑] 包含可重现的代码

我正在尝试运行一个 while 循环，我使用的条件是当变量e==None。相关代码如下：

    print("\nThe current score list contains the following people's scores: ")
    score_list = open("score_list.dat", "rb")
    score_name = []
    e = None
    while not e:
        try:
            score = pickle.load(score_list)
            name = pickle.load(score_list)
            score_name.append([score, name])
        except EOFError as e:
            pass            
    score_list_sorted=sorted(score_list)
    sort_list.close()
    for item in score_list_sorted:
        print("Score: ", item[0], "\t", item[1])

完整的代码在这里：https://www.dropbox.com/s/llj5xwexzfsoppv/stats_quiz_feb24_2013.py

它所需的数据文件（运行测验）位于此链接中：https://www.dropbox.com/s/70pbcb80kss2k9e/stats_quiz.dat

main()需要编辑以使用正确的数据文件地址：

我收到的完整错误消息如下。这很奇怪，因为我初始化了e就在 while 循环之前。我希望有人能帮助我解决这个问题。谢谢！

Traceback (most recent call last):
  File "<pyshell#217>", line 1, in <module>
    main()
  File "/Users/Dropbox/folder/stats_quiz_feb24_2013.py", line 83, in main
    while not e:
UnboundLocalError: local variable 'e' referenced before assignment

这个错误是由于新的try...except...作用域，这是 Python 3 的一项功能。
See PEP-3110 http://www.python.org/dev/peps/pep-3110/

在 Python 3 中，以下块

try:
    try_body
except E as N:
    except_body
...

被翻译为（Python 2.5 术语）

try:
    try_body
except E, N:
    try:
        except_body
    finally:
        N = None
        del N
...

因此，Python 3 中的这个函数

def main():
    e = None
    print(locals())
    while not e:
        try:
            raise Exception
        except Exception as e:
            pass

相当于

def main():
    e = None
    print(locals())
    if not e:
        try:
            raise Exception
        except Exception as e:
            pass
        del e
    if not e:
        try:
            raise Exception
        except Exception as e:
            pass
        del e
    ...

e已初始化，但在第一个之后已被删除try except block.
Thus, UnboundLocalError是不可避免的。