old_contents: class System:
      def __init__(self, sleep_time='1m', currency_pair='btc_jpy', api_domain='api.zaif.jp', retry_count=5):
          self._system = {'sleep_time': sleep_time, 'currency_pair': currency_pair, 'api_domain': api_domain, 'retry_count': retry_count}
  
      @property
      def sleep_time(self):
          return self._system['sleep_time']
  
      @sleep_time.setter
      def sleep_time(self, time):
          self._system['sleep_time'] = time
  
      @property
      def currency_pair(self):
          return self._system['currency_pair']
  
      @currency_pair.setter
      def currency_pair(self, pair):
          self._system['currency_pair'] = pair
  
      @property
      def api_domain(self):
          return self._system['api_domain']
  
      @property
      def retry_count(self):
          return self._system['retry_count']
  
      @retry_count.setter
      def retry_count(self, count):
          self._system['retry_count'] = count
new_contents: class System:
      def __init__(self, sleep_time='1m', currency_pair='btc_jpy', retry_count=5):
          self._system = {'sleep_time': sleep_time, 'currency_pair': currency_pair, 'retry_count': retry_count}
  
      @property
      def sleep_time(self):
          return self._system['sleep_time']
  
      @sleep_time.setter
      def sleep_time(self, time):
          self._system['sleep_time'] = time
  
      @property
      def currency_pair(self):
          return self._system['currency_pair']
  
      @currency_pair.setter
      def currency_pair(self, pair):
          self._system['currency_pair'] = pair
  
      @property
      def retry_count(self):
          return self._system['retry_count']
  
      @retry_count.setter
      def retry_count(self, count):
          self._system['retry_count'] = count
subject: delete api_domain