You should start out by verifying that sphviewer is installed on your system (I know it probably is, but it's worth the extra 5 seconds just to be sure).
pip freeze | grep sphviewer
If there's no output, then it's not installed. I noticed you didn't include sudo in your install command. Depending on how your system is configured, you may need that to successfully install the module
sudo pip install py-sphviewer
If you still can't import try entering this:
python -c "import sys; print sys.path"
This will show you where python is looking to find installed packages. The sphviewer files should be in one of the shown directories. If it's not, you'll have to see where pip installed it. In theory you can do
python -c "import pip; print pip.get_installed_distributions"
to see everything (though if you can't import the package, it might not be there either). If it's not there you'll have to find the location using other means. Once you have the containing directory, add it to your path.
Note: if you're using virtual environments, you will probably have to re-install this package in the virtual environment separately.