ImportError: No Module Named

问题:

I am trying to learn programming through Python, so I apologize in advance if this is an absurdly simple question.

I am attempting to simplify my convoluted directory structure and utilize some of Python's code-reuse features, I have encountered what is for me an inexplicable ImportError error. For the past several hours I've been reading about Python's import, module, and package features (here, here, here, and here among others), yet I remain unable to solve this (seemingly) simple error.

Here is the problem.

I have one directory (dir), within which resides one sub-directory (subdir). Each directory includes a few files. Thus, my overall directory structure looks like the following:

dir/
    __init__.py
    draw_lib.py
    subdir/
        __init___.py
        drawing.py

In my drawing.py file, I attempt to import draw_lib.py with the following line: from dir import daw_lib.py. It results in an ImportError: No module named dir. Can anyone provide a quick explanation for why my drawing.py file can't find my dir directory? Thank you for any assistance. I'm completely lost and would really like to improve my code reuse and directory structure once and for all.

回答1:

You are initially executing draw_lib.py. So the 'root directory' is / throughout the program.

Then, when you attempt 'from dir import draw_lib.py' in drawing.py it wont work because the root directory is still / and not dir/.

import draw_lib

Will work in drawing.py.

Example:

/
    __init__.py
    main.py
    test/
        __init___.py
        case.py

In main.py, put this:

import test.case

print 'main.py'

if __name__ == "__main__":
        test.case.test()

In test/case.py, put this:

import main

def test():
        print 'case.py'

My output:

main.py
main.py
case.py

As you can see, I imported main.py from a nested file. You'll see main.py two times. Once for the initial startup the second time when you import it in case.py.