aws s3api list-objects-v2
--bucket myBucket
--prefix path1/path2
--query 'reverse(sort_by(Contents,&LastModified))[0]'

keys=[]
kwargs = {'Bucket': bucket_name, 'Prefix': key}
  while True:
      resp = get_conn().list_objects_v2(**kwargs)
      keys.append(sorted(response['Contents'], key=lambda item: item['LastModified'])[-1])

      try:
          kwargs['ContinuationToken'] = resp['NextContinuationToken']
      except KeyError:
          break

import boto3

client = boto3.client('s3',region_name='ap-southeast-2')

response = client.list_objects_v2(Bucket='my-bucket')

print (sorted(response['Contents'], key=lambda item: item['LastModified'])[-1])