Perhaps the 'atpy' package depends on another package called 'astropy.io' that you are missing? Yes here it is https://astropy.readthedocs.org/en/v0.1/index.html
It happens that downloading the tar balls from pypi.python.org is the wrong way to install Python packages. The right way (though the Python docs explain poorly), is to run a command like
pip install atpy
This command will install your package and all its dependencies.
If the command pip
is missing, you have to install it, which is ironically really complicated.