实例化后在Currency类内部创建动态SpecificAsset类的实现问题

核心问题梳理 #

• create_asset_class作为Currency的实例方法，缺少self参数
• 动态类的父类直接指定为SpecificAsset即可，其绑定的元类会自动被继承，无需额外配置
• 自定义__init__逻辑存在错误：未定义argnames参数、调用父类__init__时传参不符合要求
• 动态类命名逻辑错误，误用了self.name而不是传入的name参数

修正后的可运行代码 #

from datetime import datetime
from decimal import Decimal

class AssetMeta(type):
    asset_classes = {}
    
    def __new__(cls, clsname, superclasses, attributedict):
        if clsname in cls.asset_classes:
            raise ValueError("Redefinition of Asset subclass '{}'".format(clsname))
        tp = type.__new__(cls, clsname, superclasses, attributedict)
        cls.asset_classes[clsname] = tp
        return tp

class SpecificAsset(metaclass=AssetMeta):
    def __init__(self, owner, priAssetType, priAsset, qty, altAsset):
        self.id                  = id(self)
        self.owner               = owner
        self.creationDate        = datetime.now()
        
        self.priType             = priAssetType
        self.primary             = priAsset
        self.holdingQty          = Decimal(qty)
        self.initialQty          = Decimal(qty)
        self.primary.holdingQty += Decimal(qty)
        
        self.altType             = 'quote' if self.priType == 'base' else 'base'
        self.alternate           = altAsset
        self.altValue            = Decimal('0.00')
        
        self.USDpointer          = getattr(self.primary, 'pointer', None)
        self.pending             = False

class Currency:
    count = 0
    def __init__(self, name):
        Currency.count += 1
        self.id         = id(self)
        self.name       = name
        self.bases      = {}
        self.quotes     = {}
        self.holdingQty = Decimal('0.00')
        self.pointer    = None
        
    def point_to(self, CUR):
        self.pointer    = CUR
   
    def create_asset_class(self, name, BaseClass=SpecificAsset):
        # 可选优化：自动填充priAsset为当前Currency实例，减少调用传参
        def __init__(self, owner, priAssetType, qty, altAsset, priAsset=None):
            priAsset = priAsset or self
            super().__init__(owner, priAssetType, priAsset, qty, altAsset)
        # 父类直接填BaseClass即可，元类会自动继承
        newclass = type(name, (BaseClass,), {"__init__": __init__})
        return newclass

使用示例 #

# 初始化币种
btc = Currency('BTC')
usdt = Currency('USDT')
# 为BTC-USDT交易对创建专属资产类
BTC_USDT_Asset = btc.create_asset_class(name='BTC_USDT_Asset')
# 实例化资产类（对应买入操作）
owner = None # 替换为实际的Owner类实例
asset = BTC_USDT_Asset(
    owner=owner,
    priAssetType='base',
    qty='0.1',
    altAsset=usdt
)
# 验证属性
print(asset.primary.name) # 输出 BTC
print(asset.holdingQty) # 输出 0.1
print(btc.holdingQty) # 输出 0.1

扩展说明 #

• 如果需要为动态生成的资产类添加专属方法/属性，直接在type创建类的第三个参数字典中添加即可
• 元类AssetMeta已内置同名类重复创建的校验，无需额外加判断逻辑
• 不需要自动填充priAsset的话可以删掉自定义的__init__，直接继承父类的初始化逻辑即可

内容的提问来源于stack exchange，提问作者Eric