old_contents: class Trade(object):
      def __init__(self, symbol, quantity, price, buyer_id, seller_id):
          self.symbol = symbol
          self.quantity = quantity
          self.price = price
          self.buyer_id = buyer_id
          self.seller_id = seller_id
  
new_contents: class Trade(object):
      def __init__(self, symbol, quantity, price, buyer_id, seller_id):
          self.symbol = symbol
          self.quantity = quantity
          self.price = price
          self.buyer_id = buyer_id
          self.seller_id = seller_id
  
      def __repr__(self):
          return "Trade(symbol={0}, quantity={1}, price={2}, buyer_id={3}, seller_id={4})".format(
              self.symbol, self.quantity, self.price, self.buyer_id, self.seller_id)
  
subject: add __repr__ for Trade