There are at least 3 Python packages that answer to the name snappy, so it is all too easy to end up with conflicting packages. It can be helpful to mention your OS and Python version, see: How to report bugs effectively.
Did you install SNAP snappy using <snap_install_dir>/bin/snappy-conf? Can you run the provided test and example scripts (note that some tests require downloading a data file)?
Try searching the forum for previous reports such as this link.