• AmazonS3FullAccess

import json
import boto3

s3 = boto3.client("s3")

bucket = "sksmsansdj"
file_name = "/tmp/target.txt"

def lambda_handler(event, context):
    record = event["Records"][0]
    key = record["s3"]["object"]["key"]

    s3.download_file(bucket, key, file_name)

    with open(file_name, "a") as f:
        pass

    s3.upload_file(file_name, bucket, key)

    return json.dumps({"success": "OK!"})