多次导入同一模块
几个小时后，我发现了我的应用程序中出现错误的原因。我的应用程序的源代码结构如下：
main/
__init__.py
folderA/
__init__.py
fileA.py
fileB.py
确实，还有大约 50 个文件。但这不是重点。在 main/__init__.py 中，我有以下代码： fromfolderA.fileA import *
in folderA/__init__.py 我有以下代码：
sys.path.append(pathToFolderA)
在 folderA/fileB.py 我有这样的代码：
from fileA import *
问题是 fileA 被导入两次。但是，我只想导入一次。
解决这个问题的明显方法（至少对我来说）是将某些路径从 path 更改为 folderA.path
但我觉得 Python 甚至不应该在第一个错误出现地方。还有哪些其他解决方法不需要每个文件知道其绝对位置？
So after a few hours, I discovered the cause of a bug in my application. My app's source is structured like:
main/
__init__.py
folderA/
__init__.py
fileA.py
fileB.py
Really, there are about 50 more files. But that's not the point. In main/__init__.py, I have this code: from folderA.fileA import *
in folderA/__init__.py I have this code:
sys.path.append(pathToFolderA)
in folderA/fileB.py I have this code:
from fileA import *
The problem is that fileA gets imported twice. However, I only want to import it once.
The obvious way to fix this (to me atleast) is to change certain paths from path to folderA.path
But I feel like Python should not even have this error in the first place. What other workarounds are there that don't require each file to know its absolute location?
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不要以这种方式修改 sys.path，因为它提供了两种访问模块的方式（名称），从而导致您的问题。
请改用绝对导入或明确相对导入。 （不明确的相对导入可以用作较旧 Python 版本的最后手段。）
folderA/fileB.py
当然，您应该使用特定名称来代替该星号。
Don't modify sys.path this way, as it provides two ways (names) to access your modules, leading to your problem.
Use absolute or unambiguous-relative imports instead. (The ambiguous-relative imports can be used as a last resort with older Python versions.)
folderA/fileB.py
Of course, you should be using specific names in place of that star.
修改
sys.path不是您在真实程序中所做的事情。与永久设置 PYTHONPATH 或将模块放在 Python 可以找到的位置相比，它会损害模块化和可移植性。永远不要使用
import *。它会污染您的命名空间并使您的代码变得不可预测。您不希望将folderA放在
sys.path上。它是main的子包，并且应始终如此对待。始终使用绝对导入到顶级包：import main.folderA而不是importfolderA或其他任何内容；它将使您的代码更容易跟踪、移动和安装。Modifying
sys.pathisn't something you do in a real program. It hurts modularity and portability with no gain over setting PYTHONPATH permanently or putting your module in a place Python can find it.Never ever ever ever use
import *. It pollutes your namespace and makes your code unpredictable.You don't want folderA on
sys.path. It is a subpackage ofmainand should always be treated as such. Always use absolute imports going to top-level packages:import main.folderArather thanimport folderAor anything else; it will make your code a lot easier to follow and move around and install.