Q:

python import fails even if __init__.py is present

suppose i have this directory structure
package /
         __init__.py
         cpackage.py

        subpackage1/
                    __init__.py
                    subpack1_call.py

                    /lib
                        __init__.py
                        sub_lib.py
        subpackage2/
                    __init__.py
                    subpack2_call.py

i want to import cpackage in subpackage1 and subpackage2 which i am unable to import 
i get valuename error and module not found errors
where as i can easily do this in subpackage1
from lib.sub_lib import hello_pr

hello_pr() 

here there is no error and hello_pr prints what i defined in sub_lib
but i am unable to move up the directory, where as in above case i can easily move 
down the directory structure
what am i missing . i have looked into so many solutions in this site and pydoc, maybe i am missing something, cause nothing seemed to be working for

A:

If you can import lib.sub_lib, it means your PYTHONPATH points to subpackage1. It should point to the directory containing package, then you'll be able to import package.cpackage, package.subpackage1.lib.sub_lib, etc.
You can also point your PYTHONPATH to cpackage, then remove init.py in this directory as it's useless, and you can import cpackage, subpackage1.lib.sub_lib, etc.
The basic rule is: if PYTHONPATH=dir, then
dir\
  bob.py
  sub\
    __init__.py
    bib.py
    inner\
      __init__.py
      bub.py

import bob
import sub       (will import sub\__init__.py)
import sub.bib   (will import sub\__init__.py then bib.py)
import sub.inner (will import sub\__init__.py then sub\inner\__init__.py)
import sub.inner.bub (will import sub\__init__.py then sub\inner\__init__.py
                      and finally bub.py)

