AMI Deletion

import boto3
from datetime import datetime, timedelta
import datetime
import dateutil
def lambda_handler(event, context):
    retention_date=datetime.datetime.now() - datetime.timedelta(days=7)
    client = boto3.client('ec2')
    response = client.describe_images( Filters = [ { 'Name':'tag:delete','Values':["yes"] } ], Owners=['123123123123'] )
    images = response['Images']
    for i in images:
        creation_date = datetime.datetime.strptime(i['CreationDate'],"%Y-%m-%dT%H:%M:%S.000Z")
        image_id = i['ImageId']
        if creation_date < retention_date:
            print "%s deleted" % (image_id)
            res = client.deregister_image(ImageId=image_id,DryRun=False)
            print res