anchor.diff:      dest='single_node',
   )
   
  +parser.add_option(
  +    '--classes',
  +    help='List the available classes',
  +    action='store_true',
  +    dest='classes',
  +)
  +
   if __name__ == '__main__':
       main()
   
  
positive.code: def main():
      opts, args = parser.parse_args()
  
      if opts.node_class:
          if any('-' in c for c in opts.node_class):
              parser.error('Node classes should not use hyphens. Hint: Try an underscore')
  
  
negative.code: 
      return(hosts)
  
  def ec2_classes(stackname):
      client = boto3.client('ec2', region_name=region)
  
      response = client.describe_instances(
             Filters=[
                {'Name': 'tag:aws_stackname', 'Values': [stackname]},
                {'Name': 'instance-state-name','Values': ['running']}
             ]
         )
  
      nodes = response['Reservations']
  
      classes = []
      for instance in nodes:
      classes.append(filter(lambda t: t['Key'] == 'aws_migration', instance['Instances'][0]['Tags'])[0]['Value'])
  
      return(sorted(set(classes)))
  
  def get_hostname_by_id(instance_id):
      client = boto3.client('ec2', region_name=region)
      response = client.describe_instances(InstanceIds=[instance_id])
  