packages - Python subpackage in arbitrary folder. How to write the __init_

if have hierarchy

a |- __init__.py |-b   |- __init__.py   |- funcitons.py       (which contains def my_function(): pass)

and have package a installed, can following

from a.b import functions functions.my_function()

from a.b.functions import my_function my_function()

how accomplish same result if b encapsulated in several subfolders (which not packages)?

as suggested antti haapala, in python 2 __path__ for. following a/__init__.py did job.

import os __path__.append( os.path.join(os.path.dirname(__file__), 'res/path'))

TY