如何从 Python 中的子 class 调用和覆盖父 class 方法

Question

在 ResistantVirus class 的 reproduce 方法中，我试图调用 SimpleVirus class 的 reproduce(self, popDensity)，但是相反return 一个 SimpleVirus 对象，我希望它 return 一个 ResistantVirus 对象。

显然，我也可以重复 SimpleVirus.reproduce 方法中的一些代码并在我的 ResistantVirus.reproduce 方法中使用相同的实现，但我想知道是否可以调用和覆盖 SimpleVirus.reproduce为了避免重复？

class SimpleVirus(object):

    def __init__(self, maxBirthProb, clearProb):
        self.maxBirthProb = maxBirthProb
        self.clearProb = clearProb

    def reproduce(self, popDensity):
        if random.random() > self.maxBirthProb * (1 - popDensity):
            raise NoChildException('In reproduce()')
        return SimpleVirus(self.getMaxBirthProb(), self.getClearProb())


class ResistantVirus(SimpleVirus):

    def __init__(self, maxBirthProb, clearProb, resistances, mutProb):
        SimpleVirus.__init__(self, maxBirthProb, clearProb)
        self.resistances = resistances
        self.mutProb = mutProb

    def reproduce(self, popDensity)       

      ## returns a new instance of the ResistantVirus class representing the       
      ## offspring of this virus particle. The child should have the same   
      ## maxBirthProb and clearProb values as this virus.

      ## what I sketched out so far and probs has some mistakes:
      for drug in activeDrugs:
          if not self.isResistantTo(drug):
              raise NoChildException
              break

      simple_virus = SimpleVirus.reproduce(self,popDensity)

      return ResistantVirus(simple_virus.getMaxBirthProb(),simple_virus.getClearProb())

Answer 1

使用super调用父class'方法：

class ResistantVirus(SimpleVirus):
    def __init__(self, maxBirthProb, clearProb, resistances, mutProb):
        self.resistances = resistances
        self.mutProb = mutProb
        super(ResistantVirus, self).__init__(maxBirthProb, clearProb)

    def reproduce(self, popDensity):
        simple_virus = super(ResistantVirus, self).reproduce(popDensity)
        resistances = # TODO
        mutProb = # TODO
        return ResistantVirus(simple_virus.maxBirthProb,
                              simple_virus.clearProb, 
                              resistances, 
                              mutProb)

Answer 2

看来 copy 可以帮到你。

import copy

class Parent(object):
    def __init__(self, a):
        self.a = a

    def copy(self):
        return copy.deepcopy(self)

class Child(Parent):
    def __init__(self, a, b):
        super(Child, self).__init__(a)
        self.b = b

copy 方法将携带任何 self 的 class（不一定是 Parent）。例如：

Child(1,2).copy() # <__main__.Child object at 0x01832E90>

这似乎是您的主要目标。但是，在如何构建测试方面也可能值得付出一些努力。我已经使用您的示例代码实现了一个不同的解决方案，允许您继承测试。请注意，这要求您向病毒传递一个关键字参数列表 (**kwargs)。后面给出了示例用法。

import copy, random

class SimpleVirus(object):

    def __init__(self, max_birth_prob, clear_prob):
        self.max_birth_prob = max_birth_prob
        self.clear_prob = clear_prob
        self._tests = [self.simple_test]

    def copy(self):
        return copy.deepcopy(self)

    def simple_test(self, **kwargs):
        return random.random() < self.max_birth_prob * (1 - kwargs['pop_density'])

    def reproduce(self, **kwargs):
        if all(test(**kwargs) for test in self._tests):
            return self.copy()
        raise Exception


class ResistantVirus(SimpleVirus):

    def __init__(self, max_birth_prob, clear_prob, resistances, mut_prob):

        super(ResistantVirus, self).__init__(max_birth_prob, clear_prob)
        self.resistances = resistances
        self.mut_prob = mut_prob
        self._tests.append(self.resistance_test)

    def resistance_test(self, **kwargs):
        return all(drug in self.resistances for drug in kwargs['drug_list'])

以下内容有时会重现，有时会引发 Exception。

res_virus = ResistantVirus(0.8, 0.2, ['a', 'b', 'c'], 0.1)
res_virus.reproduce(pop_density=0.3, drug_list=['a', 'b'])

请注意，两个 classes 之间没有明显的代码重用。如果你有一个严格的继承链并且事情趋于 "build-up" 这很好。但是，如果您要有很多 classes 都继承 SimpleVirus，并且其中一些 classes 共享功能，那么 object composition over inheritance 可能值得一看.

Answer 3

只要 __init__() 签名兼容，您就可以使用实例的类型而不是显式类型。

class Parent(object):
    def __str__(self):
        return 'I am a Parent'

    def reproduce(self):
        # do stuff common to all subclasses.
        print('parent reproduction')
        # then return an instance of the caller's type
        return type(self)()

class Child(Parent):
    def __str__(self):
        return 'I am a Child'

    def reproduce(self):
        # do stuff specific to Child.
        print('child reproduction')
        # call the parent's method but it will return a
        # Child object
        return super(Child, self).reproduce()


print(Parent().reproduce())

parent reproduction    
I am a Parent

print(Child().reproduce())

child reproduction
parent reproduction
I am a child

如何从 Python 中的子 class 调用和覆盖父 class 方法

How to call and override a Parent class method from Child class in Python

python

oop

inheritance

parent-child

python-2.7