Adding Cassandra Data source in redash

I have tried to add Cassandra in redash but whenever i am adding anything in script such as
from redash.query_runner import BaseQueryRunner

class Snowflake(BaseQueryRunner):
def run_query(self, query, user):
pass

in query runner file it got stop in fronted.
help me to add cassandra in redash.
Thanks in advance.

Can you be more specific about this being stopped in the front-end?