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):

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?