relative imports and sub-module execution

[King]

Hi,

After reading couple of docs and articles, I have implemented a simple
test package with nested modules.
When running "main.py", everything is working fine. Some of my sub-
modules has some small test routines for debug purpose.
It's because I am using relative package imports at the top, I am not
able to run these sub modules individually.

For example, this works when running from main.py

Here is example structure

main.py
__init__.py
core/
__init__.py
folder1
__init__.py
f1a.py
f1b.py
folder2
__init__.py
f2a.py
f2b.py

in folder2/f2b.py, I am importing

from core.folder1 import f1a
print f1a.myvar

Now I can't execute 'f2b.py' individually. It's giving an error:

ImportError: No module named core.folder2

Is this mean when you have created a package where modules are using
relative imports, they can't execute individually?

Another solution that I have discovered is using sys.path. Check this:

import sys
import os
sys.path.append(os.path.abspath("../../"))
from core.folder1 import f1a
print f1a.myvar

This works fine and easier too. I can execute modules individually as
well as package is also working. Are there any disadvantages when
using above technique? Couple of articles suggests that this is a bad
practice and should not be used.

Need some clarifications.

Thanks

Prashant

 

[Diez B. Roggisch]

Hi,

After reading couple of docs and articles, I have implemented a simple
test package with nested modules.
When running "main.py", everything is working fine. Some of my sub-
modules has some small test routines for debug purpose.
It's because I am using relative package imports at the top, I am not
able to run these sub modules individually.

For example, this works when running from main.py

Here is example structure

main.py
__init__.py
core/
__init__.py
folder1
__init__.py
f1a.py
f1b.py
folder2
__init__.py
f2a.py
f2b.py

in folder2/f2b.py, I am importing

from core.folder1 import f1a
print f1a.myvar

Now I can't execute 'f2b.py' individually. It's giving an error:

ImportError: No module named core.folder2

Is this mean when you have created a package where modules are using
relative imports, they can't execute individually?

The problem is your python-path. Python will put the path of the script
that you execute into the sys.path - but not attempt to guess that you
actually are deep within a package hierarchy and want the path two up
from there in sys.path as well. Which is the reason why you have to do
that yourself.

My solution to this is to always use setuptools, even for the
tiniest of projects, and simply create a setup.py with some minimal
information in it, and then do

python setup.py develop

This will put a EGG-link into the site-packages directory. Usually, for
not clobbering my system's python, I use a virtualenv also.

With this setup, I can safely import from "core" all the time.

Diez