code: def contains_one_of(*fields):
      
      message = 'Must contain any one of the following fields: {0}'.format(', '.join(fields))
  
      def check_contains(endpoint_fields):
          for field in fields:
              if field in endpoint_fields:
                  return
  
          errors = {}
          for field in fields:
              errors[field] = 'one of these must have a value'
          return errors
      check_contains.__doc__ = message
      return check_contains
docs: Enables ensuring that one of multiple optional fields is set