python中全局变量的困惑
我是Python新手，所以请原谅这可能是一个非常愚蠢的问题。
基本上，我有一个名为 _debug 的全局变量，用于确定脚本是否应输出调试信息。 我的问题是，我无法在与使用它的脚本不同的 python 脚本中设置它。
我有两个脚本：
one.py:
-------
def my_function():
if _debug:
print "debugging!"
two.py:
-------
from one import *
_debug = False
my_function()
运行two.py 会生成错误：
NameError: global name '_debug' is not defined
任何人都可以告诉我我做错了什么吗？
I'm new to python, so please excuse what is probably a pretty dumb question.
Basically, I have a single global variable, called _debug, which is used to determine whether or not the script should output debugging information. My problem is, I can't set it in a different python script than the one that uses it.
I have two scripts:
one.py:
-------
def my_function():
if _debug:
print "debugging!"
two.py:
-------
from one import *
_debug = False
my_function()
Running two.py generates an error:
NameError: global name '_debug' is not defined
Can anyone tell me what I'm doing wrong?
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评论（4）
恐怕还有更多的问题不仅仅是前导下划线。
当您调用
my_function()时，它的命名空间中仍然不会包含您的debug变量，除非您从two.py导入它。当然，这样做意味着您最终会遇到循环依赖关系（
one.py -> Two.py -> one.py），并且您会得到NameErrorcode>s 除非您重构导入和声明各种内容的位置。一种解决方案是创建一个简单的第三个模块，它定义这样的“常量”，可以从任何地方安全地导入它，例如：
但是，我建议仅使用内置的 logging 模块 - 为什么不呢？ 它易于配置、使用更简单、可靠、灵活且可扩展。
There are more problems than just the leading underscore I'm afraid.
When you call
my_function(), it still won't have yourdebugvariable in its namespace, unless you import it fromtwo.py.Of course, doing that means you'll end up with cyclic dependencies (
one.py -> two.py -> one.py), and you'll getNameErrors unless you refactor where various things are imported and declared.One solution would be to create a simple third module which defines 'constants' like this, which can be safely imported from anywhere, e.g.:
However, I would recommend just using the built in logging module for this - why not? It's easy to configure, simpler to use, reliable, flexible and extensible.
以下划线开头的名称不会导入
Names beginning with an underscore aren't imported with
您还可以使用 __debug__ 变量进行调试。 如果解释器不是使用 -O 选项启动的，则确实如此。 断言语句也可能有帮助。
You can also use the
__debug__variable for debugging. It is true if the interpreter wasn't started with the -O option. The assert statement might be helpful, too.更多解释：函数
my_function的命名空间始终位于模块one中。 这意味着，当在my_function中找不到名称_debug时，它会在one中查找，而不是在调用该函数的命名空间中查找。 Alabaster的回答提供了一个很好的解决方案。A bit more explanation: The function
my_function's namespace is always in the moduleone. This means that when the name_debugis not found inmy_function, it looks inone, not the namespace from which the function is called. Alabaster's answer provides a good solution.