第28课按老师同样的代码输入，结果出现标题所示错误，请大家帮解答！谢谢
class TradeData:
def _init_(self):
self.symbol = symbol
self.datetime = datetime
self.direction = direction
self.price = price
self.volume = volume
def calculate_trading_value(self, size):
"""计算成交金额的对象方法"""
value = self.price * self.volume * size
return value
def to_str(self):
""""""
text = f"{self.datetime}: {self.direction} {self.symbol} {self.volume}手"@{self.price}"
return text
def _str(self):
""""""
return self.to_str()
Cell In[3], line 17
text = f"{self.datetime}: {self.direction} {self.symbol} {self.volume}手"@{self.price}"
^
SyntaxError: unterminated string literal (detected at line 17)
