new_contents: #!/usr/bin/env python2
  
  import argparse
  import yaml
  import sys
  
  parser = argparse.ArgumentParser(
          description='Insert a key-value pair into each mapping '
          'in a YAML sequence of mappings')
  parser.add_argument('key', help='Add this key')
  parser.add_argument('value', help='with this value')
  args = parser.parse_args()
  
  # Load YAML from standard in
  data = yaml.safe_load(sys.stdin)
  
  if type(data) is list:
      for d in data:
          d[args.key] = args.value
      print(yaml.safe_dump(data, default_flow_style=False))
  
  else:
      print("Error: data is not a YAML sequence")
      sys.exit(1)
  
subject: add yamladd