The version of Cassandra that you are using is only compatible with Python 2.x.
The following syntax:
except ImportError, e:
was deprecated in Python 2.7 and removed in Python 3.x. Nowadays, you use the as keyword:
except ImportError as e:
This means that you need to either downgrade to Python 2.x or get a version of Cassandra that is compatible with Python 3.x.