This requires `boto3` and `pymongo` in pip, also you need to run `aws configure` to be done.

find-latest-object-in-bucket.py

import boto3
import sys
from bson import json_util
import json
from datetime import datetime

def take_last_modified(obj):
    return obj.last_modified

def bucket_last_modified(bucket_name: str) -> datetime:
    """
    Given an S3 bucket, returns the last time that any of its objects was
    modified, as a timezone-aware datetime.
    """
    s3 = boto3.resource('s3')
    bucket = s3.Bucket(bucket_name)
    objects = list(bucket.objects.all())

    max_date = max(obj.last_modified for obj in objects)
    objects.sort(key=take_last_modified, reverse=True)
    return {
        "bucket_name": objects[0].bucket_name,
        "key": objects[0].key,
        "last_modified": objects[0].last_modified
    }

if __name__ == "__main__":
    bucket = sys.argv[1]
    print("Start digging %s" % (bucket))
    print("The last modifed object is: %s" % (
        json.dumps(bucket_last_modified(bucket), default=json_util.default)
    ))