code: def setup(self):
          
          global cluster, session
  
          if 'username' in self.cluster_options or 'password' in self.cluster_options:
              raise CQLEngineException("Username & Password are now handled by using the native driver's auth_provider")
  
          if self.lazy_connect:
              return
  
          self.cluster = Cluster(self.hosts, **self.cluster_options)
          try:
              self.session = self.cluster.connect()
              log.debug(format_log_context("connection initialized with internally created session", connection=self.name))
          except NoHostAvailable:
              if self.retry_connect:
                  log.warning(format_log_context("connect failed, setting up for re-attempt on first use", connection=self.name))
                  self.lazy_connect = True
              raise
  
          if self.consistency is not None:
              self.session.default_consistency_level = self.consistency
  
          if DEFAULT_CONNECTION in _connections and _connections[DEFAULT_CONNECTION] == self:
              cluster = _connections[DEFAULT_CONNECTION].cluster
              session = _connections[DEFAULT_CONNECTION].session
  
          self.setup_session()
docs: Setup the connection