$ find . -type f -name "*.py"
./setup.py
./mypkg/__init__.py
./mypkg/config.py
./mypkg/shapes/__init__.py
./mypkg/shapes/square.py

$ find . -type f -name "*.py" | xargs head -n999
==> ./setup.py <==
from setuptools import setup, find_packages
setup(
    name="mypkg",
    version="0.1",
    packages=find_packages(),
)

==> ./mypkg/__init__.py <==

==> ./mypkg/config.py <==
SIZE = 4

==> ./mypkg/shapes/__init__.py <==

==> ./mypkg/shapes/square.py <==
from mypkg.config import SIZE

def square(size=SIZE):
    edge = "*"*size
    inside = "*" + " " * (size-2) + "*"
    yield edge
    for i in range(size-2):
        yield inside
    yield edge

if __name__ == "__main__":
    print "\n".join(square())

$ virtualenv ~/foo-env
New python executable in /Users/stevek/foo-env/bin/python
Installing setuptools, pip...done.

$ ~/foo-env/bin/python setup.py develop
...
Finished processing dependencies for mypkg==0.1

$ ~/foo-env/bin/python mypkg/shapes/square.py
****
*  *
*  *
****