def object_summary_load(self, *args, **kwargs):
    """
    Calls s3.Client.head_object to update the attributes of the ObjectSummary
    resource.
    """
    response = self.meta.client.head_object(
        Bucket=self.bucket_name, Key=self.key
    )
    if 'ContentLength' in response:
        response['Size'] = response.pop('ContentLength')
    self.meta.data = response

    Calls s3.Client.head_object to update the attributes of the ObjectSummary
    resource.
    
boto3/s3/inject.py