How to develop programs with Python Namespaced Packages?

In Python, a namespace package allows you to spread Python code among several projects. This is useful when you want to release related libraries as separate downloads. For example, with the directories Package-1 and Package-2 in PYTHONPATH,

Package-1/namespace/__init__.py
Package-1/namespace/module1/__init__.py
Package-2/namespace/__init__.py
Package-2/namespace/module2/__init__.py
the end-user can import namespace.module1 and import namespace.module2.

On Python 3.3, you don't have to do anything, just don't put any __init__.py in your namespace package directories and it will just work. This is because Python 3.3 introduces implicit namespace packages.

On older versions, there's a standard module, called pkgutil, with which you can 'append' modules to a given namespace. You should put those two lines in both Package-1/namespace/__init__.py and Package-2/namespace/__init__.py:
from pkgutil import extend_path
__path__ = extend_path(__path__, __name__)

This will add to the package's __path__ all subdirectories of directories on sys.path named after the package. After this you can distribute the 2 packages separately and leverage python namespaced packages.