Python跨模块和全局变量导入 [英] Python imports across modules and global variables

问题描述

我有一个似乎相当基本的问题，但我似乎无法在任何地方找到任何帮助。

I have a question which seems to be rather fundamental but I can't seem to find any help on this anywhere.

file_a.py >>

from xyz import XYZ
class A:
    .
    .
    .

file_b.py >>

import file_a
from file_a import A
class B(A):
    def __init__(self):
        A.__init__(self)

    def someMethod(self):
        XYZ.doSomething()

XYZ.doSomething（）无法说NameError：名称'XYZ'未定义
即使从file_a完成的标准导入（如'import sys'）似乎也无法使其在file_b中可用。我认为应该工作。我的理解错了吗？如果是，那么有没有办法在文件中包含常见的导入和全局变量？ （如果它有帮助，我一直是C ++和java程序员，我现在开始使用python。）

XYZ.doSomething() fails saying NameError: name 'XYZ' is not defined Even standard imports like 'import sys' done from file_a does not seem to render it usable in file_b. I assumed that should work. Is my understanding wrong? If yes, then is there a way to have common imports and global variables across files? (If it is of nay help, I've been a C++ and java programmer and am now starting to use python. )

推荐答案

我的理解错了吗？

Is my understanding wrong?

是的，因为来自file_a import的行 A 只导入 A 类 file_b 的命名空间。 file_a 的命名空间不变。如果它不是这样，那么两种语法都没有意义：

Yes, because the line from file_a import A import only class A into the namespace of file_b. The namespace of file_a is left alone. If it were not like this, there would be little sense in having both syntax:

import modulename
from modulename import something

好像你的想法是正确的，然后在第二种形式之后你总是可以使用 modulename.someotherthing 。

as if your thinking was right, then after the second form you would always be able to use modulename.someotherthing.

如果是，那么有没有办法进行常见的进口和文件中的全局变量？

If yes, then is there a way to have common imports and global variables across files?

是的，使用星号 * 运算符：

Yes, with the star * operator:

from modulename import *

但这会带来命名空间污染问题，例如来自file_a import * 的将导入 file_b 还在 file_a 中完成所有导入。你将最终失去对你的进口的控制权，这会在某个时候咬你...相信我这个！

but this brings the issue of namespace pollution, for example from file_a import * will import in file_b also all the imports done in file_a. You will eventually lose control of your imports and this will bite you at some time... trust me on this!

当出于某种原因需要来自模块导入* ，命名空间污染的解决方法是在模块中定义 变量 __ all __ ，将应导入的内容列入白名单与明星运营商合作。

When for some reason from module import * is needed, a workaround to namespace pollution is to define in module the variable __all__, which whitelists what should be imported with the star operator.

HTH！

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