Why can't I import mod1 and mod2 from the same package when they aren't in the same directory?

The Python import statement searches the PYTHONPATH for modules. If the module is a Python script file in the site-packages directory, Python will find it whereever it first appears in the PYTHONPATH.

For nested modules, those of the form Level1.Level2.Level3, the behaviour is a bit different. Nested modules, such as these, are implemented as directories within the PYTHONPATH. So Level1.Level2.Level3 maps to <some-dir-in-the-PYTHONPATH>/Level1/Level2/Level3.py. In order to load this module, the Python interpreter must first load Level1 and Level1.Level2. Once the upper level modules are loaded, the interpreter looks in the __path__ of the upper level module for all lower level modules. In other words, the interpreter will only look in the first place it found the highest level module for the lower level modules.

As of ACS 6.0.3, there is an import function that will search the entire PYTHONPATH for modules. To use it, simply add:

import AcsutilPy.ACSImport

as your first import in your Python code and all subsequent imports will search all directories.

NOTE: If the same module appears twice in the PYTHONPATH, the first one found will be loaded.

-- ArneGrimstrup - 21 Feb 2007

The new import function has been enabled in the Python container as of ACS 6.0.3. If you are using a Python component and need the searching behaviour, there is no need to modify your code.

-- ArneGrimstrup - 29 May 2007

The Python library module pkgutil provides a much more reliable method to extend the search path. Simply add:

from pkgutil import extend_path
__path__ = extend_path(__path__, __name__)

To your module's __init__.py file and all instances of that module's name in the PYTHONPATH will be included in the search. They should all be at the same level in the directory tree. For example, if your PYTHONPATH is top1:top2:top3 and you run the extension code for a module "mod" in top1, your module's search path could have top1/mod, top2/mod and top3/mod but not top2/inter/mod.