部分继承

Question

我是 Python 新手，但有一些东西让我对类继承感到疯狂，我在网上找到的所有解决方案都对我不起作用，我无法理解原因。

我有一个课程Bond，其中有一个我们将投资于它们的条款、一定的投资金额、最低价格、最低期限和年利率。子类LongTerm 的最短期限为 2 年，最低金额为 250 美元，年利率为 2.5%。

以下代码可以正常工作：

class Bond(object):
    def __init__(self,minTerm, term,amount,minPrice,yrlyRate):
        self.term = term
        self.amount = amount
        self.minPrice = minPrice
        self.minTerm = minTerm
        self.yrlyRate = yrlyRate

class LongTerm(Bond):
    def __init__(self, term,amount,minPrice, minAmount = 1000, minTerm = 5, yrlyRate = 0.05):
        self.term = term
        self.amount = amount
        self.minPrice = minPrice
        self.minAmount = minAmount
        self.minTerm = minTerm
        self.yrlyRate = yrlyRate

但是当我使用部分继承功能时

super().__init__(term,amount,minPrice)

显示错误：

TypeError: __init__() missing 2 required positional arguments: 'minPrice' and 'yrlyRate'

使用super()的代码：

class Bond(object):
    def __init__(self,minTerm, term,amount,minPrice,yrlyRate):
        self.term = term
        self.amount = amount
        self.minPrice = minPrice
        self.minTerm = minTerm
        self.yrlyRate = yrlyRate

class LongTerm(Bond):
    def __init__(self, term,amount,minPrice, minAmount = 1000, minTerm = 5, yrlyRate = 0.05):
        super().__init__(term,amount,minPrice)
        self.term = term
        self.amount = amount
        self.minPrice = minPrice

为什么我不能只部分继承超类的某些实例？

Answer 1

我认为你需要的是这样的......

class Bond:
    def __init__(self, term, amount, minPrice, minTerm, yrlyRate):
        self.term = term
        self.amount = amount
        self.minPrice = minPrice
        self.minTerm = minTerm
        self.yrlyRate = yrlyRate

    def __repr__(self):
        return f"Term: {self.term}, Amount: {self.amount}, MinPrice: {self.minPrice}, MinTerm: {self.minTerm}, YearlyRate: {self.yrlyRate}"

class LongTerm(Bond):
    def __init__(self, term, amount, minPrice, minTerm=5, yrlyRate=0.05, minAmount=1000):
        super().__init__(term=term, amount=amount, minPrice=minPrice, minTerm=minTerm, yrlyRate=yrlyRate)
        self.minAmount = minAmount

print(LongTerm(term=1, amount=23, minPrice=45.2))

Answer 2

如果您的子类需要的信息比您的超类少，那么您可能不需要使用继承。如果无法修改原始版本，那么composition 可能会更有帮助。

方法一、通用类继承

class Bond:
    def __init__(self, minTerm, term, amount, minPrice, yrlyRate):
        self.term = term
        self.amount = amount
        self.minPrice = minPrice
        self.minTerm = minTerm
        self.yrlyRate = yrlyRate


class LongTerm(Bond):
    def __init__(self, term, amount, minPrice, minAmount = 1000, minTerm = 5, yrlyRate = 0.05):
        super().__init__(minTerm, term, amount, minPrice, yrlyRate)
        self.minAmount = minAmount

方法 2)。带有覆盖示例和默认参数

class Bond:
    def __init__(self, minTerm, term, amount, minPrice, yrlyRate):
        self.term = term
        self.amount = amount
        self.minPrice = minPrice
        self.minTerm = minTerm
        self.yrlyRate = yrlyRate
    
    def short_term_only(self):
        #do some stuff

        
class LongTerm(Bond):
    def __init__(self, term, amount, minPrice, minAmount = 1000, minTerm = 5, yrlyRate = 0.05):
        # In the event that maybe we don't care about some of the information or methods
        # in the parent we can set them to none or even over-ride the methods
        super().__init__(minTerm, None, None, minPrice, yrlyRate)
        self.minAmount = minAmount
        
    def short_term_only(self):
        raise NotImplementedError

方法 3) 使用类组合。与此方法有关的问题是 methods 可用于类 Bond 将不会固有地可用于类 LongTerm

class LongTerm:
    def __init__(self, term, amount, minPrice, minAmount = 1000, minTerm = 5, yrlyRate = 0.05):
        self.bond = Bond(minTerm, term, amount, minPrice, yrlyRate)
        self.minAmount = minAmount