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The header might be quite hard to understand, but I'll try to explain as well as I can.

I have a folder called SubModule which includes total of 3 files:

__init__.py Class1.py Class2.py

Inside __init__.py, I got this:

import Class1 import Class2 def main(): c1 = Class1.Class1() c2 = Class2.Class2() if __name__ == "__main__": main()

And it all works fine with no errors, and I can use c1 and c2 properly.

The problem appears, when I try to move SubModule folder under an other module's (let's call it MainModule) folder. So I would have the following:

MainModule\__init__.py MainModule\SubModule\__init__.py MainModule\SubModule\Class1.py MainModule\SubModule\Class2.py

Now when I try to import SubModule from MainModule\__init__.py like so:

import SubModule c1 = SubModule.ClassOne.ClassOne() c2 = SubModule.ClassTwo.ClassTwo()

I would expect this to work. However, running the MainModule\__init__.py raises an error from SubModule\__init__.py:

Traceback (most recent call last): File "C:\...\MainModule\__init__.py", line 1, in <module> import SubModule File "C:\...\MainModule\SubModule\__init__.py", line 1, in <module> import Class1 ImportError: No module named 'Class1'

As you can see, the error comes from import Class1, and it tells me that there's No module named 'Class1'. This is cause the path is now SubModule.Class1, instead of only Class1. I can get rid of this error by changing SubModule\__init__.py to this:

import SubModule.Class1 import SubModule.Class2

However, I can no longer use the SubModule alone by running SubModule\__init__.py, since the path would be import Class1 again, instead of import SubModule.Class1.

This is making me crazy, is there a way to generalize the importing, so it doesn't matter which module imports SubModule?

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  • This is a strange way of doing imports. Why don't you put SubModule in one place, add it to the system path, and always import it from there? Commented Dec 1, 2012 at 20:49

2 Answers 2

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There's a way, not exactly 'general', but ...

try: import Submodule.Class1 as Class1 except ImportError: import Class1
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I won't accept yet, if someone comes up with something better, but this'll do for now. I had similar one already, but thanks for the as Class1 tip, didn't know that one.
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You should always import a module absolutely from the system path. So if your package MainModule contains a subpackage SubModule, you should do from MainModule import SubModule (or from . import SubModule). Also, inside SubModule, do from . import Class1. This should let it work regardless of the path to SubModule. (However, it will still cause weirdness if you import SubModule in two different ways -- which includes running it as the main file vs importing it.)

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That sounds somewhat better, I can't test it now but I will when I get home.
I can't import from MainModule ..., since No module named 'MainModule'