code: def reminder_validator(input_str):
      
      match = re.match(REMINDER_REGEX, input_str)
      if match or input_str == '.':
          return input_str
      else:
          raise ValidationError('Expected format: <number><w|d|h|m> '
                                '<popup|email|sms>. (Ctrl-C to exit)\n')
docs: Allows a string that matches utils.REMINDER_REGEX.
      Raises ValidationError otherwise.