title: Can't get total size of a bucket with Boto3
body: <p>I'm trying to get the total size of a bucket. However total_size returns 0. Of course there are a couple of files in the bucket. If I have five files in my bucket the following function prints five zeros. What am I doing wrong?</p>
  
  <pre><code>bucket = boto3.resource('s3', config=Config(signature_version="s3", s3={'addressing_style': 'path'})).Bucket(name)
  for object in bucket.objects.all():
      total_size += object.size
      print(object.size)
  </code></pre>