importing same module more than once

So after a few ho开发者_JAVA技巧urs, 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?

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

from main.folderA.fileA import *   # absolute
from .fileA import *               # unambiguous-relative
from fileA import *                # ambiguous-relative

Of course, you should be using specific names in place of that star.

• Modifying sys.path isn'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 of main and should always be treated as such. Always use absolute imports going to top-level packages: import main.folderA rather than import folderA or anything else; it will make your code a lot easier to follow and move around and install.