Python - Doing absolute imports from a subfolder

Hi,

Basically I'm asking the same question as this guy: http://stackoverflow.com/questions/72852/how-to-do-relative-imports-in-python

But no one gave him a correct answer. Given that you are inside a subfolder and you want to go up a directory and then into ANOTHER subfolder, doing what they suggested does not work (as the OP pointed out in his comments to their answers).

I know that you can do this by using sys.path, but I would prefer a cleaner method.

Example:

App
__init__.py
Package_A
--__init__.py
--Module_A.py
Package_B
--__init__.py
--Module_B.py

How would I import Module_A into Module_B?

From stackoverflow

• If I'm reading correctly, in Python 2.5 or higher:

  from ..Module_B import Module_B
  

  I thought I was well-versed in Python but I had no idea that was possible in version 2.5.

  bobince : That's correct. It's a bit ugly though, and absolute imports are generally the best thing except in special circumstances.

  ryeguy : THis doesn't work I get "attempted relative import in non-package"

  bobince : The statement is assumed to be inside Module_A.py (and, post-edit, should be from ..Package_B.) relative imports are based on the package path of the module you are inside, not directories; you can't use them from a top-level script or simple module.

• If you are then importing Module_B in to App, you would

  Module_B.py: import ModuleA

  App.py (which also imports ModuleA which is now by default in your Pythonpath)

  import Module_B.Module_B
  

  Another alternative, is to update __init__.py (the one in Module_A/App folder) to:

  import os
  import sys
  sys.path.extend('%s../' % os.getcwd())
  import ModuleA
  

  Another alternative, is to add your folder to the PYTHONPATH environment var.

  Aaron Gallagher : Modifying `sys.path` at runtime is nearly always wrong. It's fragile and indicates a badly-structured package.

  Nick Stinemates : I definitely agree.

• main.py
  setup.py
  app/ ->
      __init__.py
      package_a/ ->
         __init__.py
         module_a.py
      package_b/ ->
         __init__.py
         module_b.py
  

  1. You run python main.py.
  2. main.py does: import app.package_a.module_a
  3. module_a.py does import app.package_b.module_b

  Alternatively 2 or 3 could use: from app.package_a import module_a

  That will work as long as you have app in your PYTHONPATH. main.py could be anywhere then.

  So you write a setup.py to copy (install) the whole app package and subpackages to the target system's python folders, and main.py to target system's script folders.