s3bucketsizes.py

# from: http://www.slsmk.com/getting-the-size-of-an-s3-bucket-using-boto3-for-aws/
# modified to return rounded sizes in Gigabytes
# and sorted by descending total storage size

import boto3
import datetime

now = datetime.datetime.now()

cw = boto3.client('cloudwatch')
s3client = boto3.client('s3')

# Get a list of all buckets
allbuckets = s3client.list_buckets()

# Header Line for the output going to standard out
print('Bucket'.ljust(45) + 'Size in GigaBytes'.rjust(25))

bucket_sizes = []
# Iterate through each bucket
for bucket in allbuckets['Buckets']:
    # For each bucket item, look up the cooresponding metrics from CloudWatch
    response = cw.get_metric_statistics(Namespace='AWS/S3',
                                        MetricName='BucketSizeBytes',
                                        Dimensions=[
                                            {'Name': 'BucketName', 'Value': bucket['Name']},
                                            {'Name': 'StorageType', 'Value': 'StandardStorage'}
                                        ],
                                        Statistics=['Average'],
                                        Period=3600,
                                        StartTime=(now-datetime.timedelta(days=1)).isoformat(),
                                        EndTime=now.isoformat()
                                        )

    # probably empty buckets
    if len(response["Datapoints"]) == 0:
        bucket_sizes.append((bucket["Name"], 0.0))
        continue

    # The cloudwatch metrics will have the single datapoint, so we just report on it.
    for item in response["Datapoints"]:
        size_gb = float(item["Average"]) / 1024.0 / 1024.0 / 1024.0
        bucket_sizes.append((bucket["Name"], size_gb))

for bucket, size_gb in sorted(bucket_sizes, key=lambda (b, s): s, reverse=True):
    print(bucket.ljust(45) + "{:,}".format(round(size_gb, 2)).rjust(25))
    # Note the use of "{:,}".format.
    # This is a new shorthand method to format output.
    # I just discovered it recently.