如何在Python中做部分继承?

Question

我有一个类，Bond，它有一个我们将投资的期限，一定的投资金额，最低价格，最低期限和年利率。LongTerm类别的最低期限为2年，最低金额为$250，年息为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函数 时

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

显示错误:

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

代码使用super():

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

为什么我不能部分继承超类的一些实例?

Answer 1

如果子类需要的信息比超类少，那么可能不需要使用继承。在无法修改原始类的情况下，也许组合会更有帮助。

方法1。具有通用类继承

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。使用重写示例和默认参数

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。class composition

这个方法的问题是，Bond类可用的方法本质上不会对LongTerm类可用:

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

Answer 2

我想你需要的是这样的东西…

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))