When installing via pip, the __init__.py file is missing. See screenshot below.
And just to make sure it's not a configuration issue on my machine, I downloaded the wheel directly, unzipped it, and it's also missing the __init__.py file:
https://files.pythonhosted.org/packages/73/14/537d33a2dc19469743dc75eee317a9cf439497b7446928f345df086c5316/intuit_oauth-1.2.1-py2-none-any.whl
