Question

我正在经历LPTHW并且在前42（http://learnpythonthehardway.org/book/ex43.html），我认为我对is-a和has-a概念有一个很好的把握，但在研究演习中他要求我们添加列表并且对类进行了说明，使其成为一个功能更强大的脚本。我想为狗或猫添加一个列表给个人或员工，以便存储姓名的值和员工的工资情况。我不知道如何做到这一点，并使其功能，有人可以给我一个简短的例子，我想要做什么，我将从那里建立完成其余的。谢谢，下面还有代码......

我所得到的简单例子......

class Animal(object):
    pass

## Dog is-a Animal
class Dog(Animal):
   def __init__(self, name):
        ##Dog has-a name
        self.name = name
        self.doglist = []

Dog.doglist.append("Rover")

当我执行上述操作时，我收到错误'AttributeError：type object'Dog'没有属性doglist。

完整代码：

##Animal is-a object (yes, sort of confusing) look at the extra credit
class Animal(object):
    pass

## Dog is-a Animal
class Dog(Animal):
    def __init__(self, name):
        ##Dog has-a name
        self.name = name


##Cat is-a animal
class Cat(Animal):
    def __init__(self, name):
        ##Cat has-a name
        self.name = name

##Person is-a object
class Person(object):
    def __init__(self, name):
        ##Person has-a name
        self.name = name


        ##Person has-a pet
        self.pet = None


##Employee is-a Person
class Employee(Person):
    def __init__(self, name, salary):
        ## not sure what this does
        super(Employee, self).__init__(name)
        ##Person has-a salary
        self.salary = salary

##Fish is a class
class Fish(object):
    pass

##Salmon is-a fish and is a class
class Salmon(Fish):
    pass

##Halibut is-a fish
class Halibut(Fish):
    pass

##rover is-a Dog
rover = Dog("Rover")


##satan is-a Cat
satan = Cat("Satan")

##mary is a person
mary = Person("Mary")

##Mary has-a pet named satan
mary.pet = satan

##frank is-a employee that has-a salary of 120,000
frank = Employee("Frank", 120000)

##frank has-a pet rover(dog)
frank.pet = rover

##flipper is-a instance of Fish
flipper = Fish()

##crouse is-a instance of salmon
crouse = Salmon()

##harry is-a instance of Halibut
harry = Halibut()

print frank.pet.name

Answer 1

class Animal(object):
    pass

## Dog is-a Animal
class Dog(Animal):
   def __init__(self, name):
        ##Dog has-a name
        self.name = name
        self.doglist = []

Dog.doglist.append("Rover")

这不起作用的原因是因为您尚未初始化Dog对象。要纠正这个：

dog = Dog('Fido')
dog.doglist.append('Rover')

在__init__方法中设置属性时，必须先将其初始化以访问该属性，否则它不存在。如果您希望所有Dog个对象共享相同的列表，您可以：

class Dog:
    dog_list = []

    def __init__(self, name):
        self.name = name

然后

>>> Dog.dog_list.append('Fido')
>>> Dog.dog_list
['Fido']
>>> dog = Dog('Rover')
>>> dog.dog_list
['Fido']
>>> dog.dog_list.append('Rover')
>>> dog.dog_list
['Fido', 'Rover']
>>> Dog.dog_list
['Fido', 'Rover']

在方法外部声明的属性将在该类的所有实例之间共享。

使用OOP创建名称列表

1 个答案: