Python奇怪的导入行为：导入xy工作，从x import y没有

Question

I am having a simple directory structure, like that:

MyProject
--main.py
--lib #that's a directory/package
----__init__.py
----view.py
----common_lib.py
----other irrelevant modules...

In main.py:

from lib import view

causes the following error:

ImportError: cannot import name view

If instead, I write it like:

from lib.view import *

This import passes successfully, but next failure happens in view.py, in that:

from common_lib import Comments, Locations, ScreenData, ProgressSignal

causes:

ImportError: No module named 'common_lib'

And as it appears from the directory structure, common_lib.py resides in the same directory as view.py, how can it happen that it cannot be found? How does it come that 'from x import y' doesn't work, and 'from xy import *' works? ' __init__.py ' is completely empty BTW. And I am using Python 3.3 32-bit.

What is more annoying, this same program worked 2 days ago.I was testing some code in IDLE and when I thought the code was ready to include in the project, pasted it into PyDev, I was shocked by this error. I changed nothing about my directories or modules.

Also, still more strangeness, running view.py and common_lib.py as standalone (without being imported) runs just fine. It should produce the error if any issues really existed.

Thanks. Any advice is highly appreciated.

Answer 1

Since main.py is still at the top level, you need to use lib.common_lib :

from lib.common_lib import Comments, Locations, ScreenData, ProgressSignal

because the previous line from lib import view does not start looking for modules from inside lib .

Answer 2

Given:

+--main.py     # from lib import view
+--lib
   +--__init__.py
   +--common_lib.py # Comments, etc.
   +--view.py       # from .common_lib import Comments, etc.

This works:

from lib import view

And this works from view.py with a relative import to indicate common_lib is in the same package.

from .common_lib import Comments, Locations, ScreenData, ProgressSignal

Answer 3

Works for me:

danielallan@MacBook:~$mkdir myproject
danielallan@MacBook:~$cd myproject/
danielallan@MacBook:myproject$mkdir lib
danielallan@MacBook:myproject$cd lib
danielallan@MacBook:lib$touch __init__.py
danielallan@MacBook:lib$touch view.py
danielallan@MacBook:lib$touch common_lib.py
danielallan@MacBook:lib$cd ..

In [1]: from lib import view

In [2]: view
Out[2]: <module 'lib.view' from 'lib/view.pyc'>

What happens when you try that on your machine? Are you sitting in the wrong directory, or is your path not configured to find these files?