How can I transparently redirect a Python import?

Question

I'm looking for a way to emulate symlinks for Python imports. I'd like to be able to unzip the following folder structure in-place without duplicating files:

root
├─ python_lib
│  └─ my_utils
│     ├─ __init__.py
│     └─ etc.py
├─ app1
├─ app2
└─ app3
   ├─ lib
   │  ├─ __init__.py
   │  └─ my_utils.py
   └─ run.py

app3/run.py contains this:

from lib.my_utils import etc

etc.pancakes()

I'd like the code to use the etc located in python_lib/my_utils/. Is there anything I can put in app3/lib/my_utils.py so that Python >= 3.1 will transparently import the python_lib/my_utils/ folder (using relative paths and ..), and subpackages will also work?

Answer 1

You will have to execute something before app3/run.py reaches the import statement.

import python_lib
import sys
sys.modules['lib'] = python_lib
# ...
from lib import etc
print etc.__file__
print dir(etc)

Answer 2

You should add this path into sys.path. For example:

lib_path = os.path.abspath( os.path.split( os.getcwd()+"/"+sys.argv[0] )[0]+"/../_lib/my_utils/" )
sys.path.append(lib_path)