Как передать список в сообщение SNS?

Попробуйте это:

message = { "source": "datapipeline",
            "application_nm": "omni",
            "severity": "2",
            "batch_run_start_dttm": "$actualStartTime",
            "batch_run_end_dttm": "actualEndTime",
            "batch_run_status_cd": "failed",
            "job_orchestration_id": "NA",
            "stage_nm": "NA",
            "stage_start_dttm": "NA",
            "stage_end_dttm": "NA",
            "stage_status_cd":  "failed",
            "job_run_id": "NA",
            "source_nm": "NA",
            "target_nm": "NA",
            "source_details": "NA",
            "target_details": "NA",
            "msg": "These mentioned hours having difference more than 50% from previous week:" +"%s"  ,
            "counts":"0",
            "notes": "After hourly comparison check, the above mentioned hours is having difference more than 50%",
            "list": list # this is how to do it
          }

Кстати, очень плохая идея назвать переменную «list», которая конфликтует со встроенной функцией list().