如何在不提供参数的情况下在 Python 中实例化一个新的数据类实例？

Question

I want to create a data class instance and supply values later.

How can I do this?

def create_trade_data():
    trades = []
    td = TradeData()
    td.Symbol='New'
    trades.append(td)
    return trades

DataClass:

from dataclasses import dataclass

@dataclass
class TradeData:
    Symbol : str
    ExecPrice : float

Answer 1

You have to make the attributes optional by giving them a default value None

from dataclasses import dataclass

@dataclass
class TradeData:
    Symbol: str = None
    ExecPrice: float = None

Then your create_trade_data function would return

[TradeData(Symbol='New', ExecPrice=None)]

Now, I chose None as the default value to indicate a lack of content. Of course, you could choose more sensible defaults like in the other answer.

Answer 2

from dataclasses import dataclass

@dataclass
class TradeData:
    Symbol : str = ''
    ExecPrice : float = 0.0

With the = operator you can assign default values. There is the field method which is used for mutable values, like list.