如何创建多个继承class的实例？

Question

我有这个代码：

class Person:
    def __init__(self, name, last_name, age):
        self.name = name
        self.last_name = last_name
        self.age = age 

class Student(Person):
    def __init__(self, name, last_name, age, indexNr, notes):
        super().__init__(name, last_name, age)
        self.indexNr = indexNr
        self.notes = notes

class Employee(Person):
    def __init__(self, name, last_name, age, salary, position):
        super().__init__(name, last_name, age)
        self.salary = salary
        self.position = position

class WorkingStudent(Student, Employee):
    def __init__(self, name, last_name, age, indexNr, notes, salary, position):
        Student.__init__(name, last_name, age, indexNr, notes)
        Employee.__init__(name, last_name, age, salary, position)

我想像这样创建一个 WorkingStudent 实例：

ws = WorkingStudent("john", "brown", 18, 1, [1,2,3], 1000, 'Programmer')

但它不起作用，我收到此错误：

TypeError: __init__() missing 1 required positional argument: 'notes'

或者我做错了什么？另外，我已经在 WorkingStudent class 中尝试过 super()，但它只调用第一个传递的 class 的构造函数。即在这种情况下 Student

注意：我已经完成了多个 Whosebug 查询，但我找不到任何可以回答这个问题的东西。（也许我错过了）。

Answer 1

这似乎可行，但并不美观。我承认我对Python中的多重继承不熟悉，我认为这可能不是最正确的方法。希望其他人能给出更好的答案。

class Person:
    def __init__(self, name, last_name, age):
        self.name = name
        self.last_name = last_name
        self.age = age


class Student(Person):
    def __init__(self, name, last_name, age, indexNr, notes):
        Person.__init__(self, name, last_name, age)
        self.indexNr = indexNr
        self.notes = notes


class Employee(Person):
    def __init__(self, name, last_name, age, salary, position):
        Person.__init__(self, name, last_name, age)
        self.salary = salary
        self.position = position


class WorkingStudent(Student, Employee):
    def __init__(self, name, last_name, age, indexNr, notes, salary, position):
        Student.__init__(self, name, last_name, age, indexNr, notes)
        Employee.__init__(self, name, last_name, age, salary, position)


ws = WorkingStudent("john", "brown", 18, 1, [1, 2, 3], 1000, 'Programmer')
print(ws)

输出：

<__main__.WorkingStudent object at 0x000002526F11F3D0>

Answer 2

而不是显式 classes，使用 super() 沿 mro 传递参数：

class Person:
    def __init__(self, name, last_name, age):
        self.name = name
        self.last_name = last_name
        self.age = age 

class Student(Person):
    def __init__(self, name, last_name, age, indexNr, notes, salary, position):
        # since Employee comes after Student in the mro, pass its arguments using super
        super().__init__(name, last_name, age, salary, position)
        self.indexNr = indexNr
        self.notes = notes

class Employee(Person):
    def __init__(self, name, last_name, age, salary, position):
        super().__init__(name, last_name, age)
        self.salary = salary
        self.position = position

class WorkingStudent(Student, Employee):
    def __init__(self, name, last_name, age, indexNr, notes, salary, position):
        # pass all arguments along the mro
        super().__init__(name, last_name, age, indexNr, notes, salary, position)

# uses positional arguments            
ws = WorkingStudent("john", "brown", 18, 1, [1,2,3], 1000, 'Programmer')
# then you can print stuff like
print(f"My name is {ws.name} {ws.last_name}. I'm a {ws.position} and I'm {ws.age} years old.")
# My name is john brown. I'm a Programmer and I'm 18 years old.

检查 mro：

WorkingStudent.__mro__
(__main__.WorkingStudent,
 __main__.Student,
 __main__.Employee,
 __main__.Person,
 object)

创建 WorkingStudent 的实例时，最好传递关键字参数，这样您就不必担心弄乱参数的顺序。

由于 WorkingStudent 将属性的定义推迟到父级 classes，立即使用 super().__init__(**kwargs) 将所有参数向上传递到层次结构中，因为子级 class 不需要知道它不处理的参数。第一个父 class 是学生，因此 self.IndexNr 等在那里定义。 mro 中的下一个父 class 是 Employee，因此从 Student 开始，将剩余的关键字参数传递给它，再次使用 super().__init__(**kwargs)。在 Employee 中，定义在那里定义的属性，然后再次通过 super().__init__(**kwargs) 将其余属性沿 mro 传递（给 Person）。

class Person:
    def __init__(self, name, last_name, age):
        self.name = name
        self.last_name = last_name
        self.age = age 

class Student(Person):
    def __init__(self, indexNr, notes, **kwargs):
        # since Employee comes after Student in the mro, pass its arguments using super
        super().__init__(**kwargs)
        self.indexNr = indexNr
        self.notes = notes

class Employee(Person):
    def __init__(self, salary, position, **kwargs):
        super().__init__(**kwargs)
        self.salary = salary
        self.position = position

class WorkingStudent(Student, Employee):
    def __init__(self, **kwargs):
        # pass all arguments along the mro
        super().__init__(**kwargs)

# keyword arguments (not positional arguments like the case above)
ws = WorkingStudent(name="john", last_name="brown", age=18, indexNr=1, notes=[1,2,3], salary=1000, position='Programmer')

Answer 3

问题：我们最派生的 class 有很多参数，需要用于初始化所有基数。但是，在 Python 的多重继承系统中 super()，接下来要初始化的 class 取决于一个 MRO（方法解析顺序），这个 MRO（方法解析顺序）可能已经在另一个 class.因此，当我们使用多重继承时，我们不知道当我们使用super()时，哪个class会调用它的__init__。

解决方法：对参数使用一致的名字，然后利用**kwargs，这样每个class就把自己关心的（明确命名的）参数拿进去，把剩下的转发出去。

看起来像：

class Person:
    def __init__(self, name, last_name, age):
        self.name = name
        self.last_name = last_name
        self.age = age 

class Student(Person):
    def __init__(self, indexNr, notes, **kwargs):
        super().__init__(**kwargs)
        self.indexNr = indexNr
        self.notes = notes

class Employee(Person):
    def __init__(self, salary, position, **kwargs):
        super().__init__(**kwargs)
        self.salary = salary
        self.position = position

class WorkingStudent(Student, Employee):
    def __init__(self, **kwargs):
        super().__init__(**kwargs)

强制客户端代码使用关键字参数对客户端来说是一项更多的工作，但它也有助于防止因弄错位置参数的顺序而导致的错误。

Answer 4

这是实现目标的最简单方法。
如果您的 WorkingStudent class 像这样继承 Student 和 Employee class，

class WorkingStudent(Student, Employee):
    def __init__(self, name, last_name, age, indexNr, notes, salary, position):
        Student.__init__(self, name, last_name, age, indexNr, notes)
        Employee.__init__(self, name, last_name, age, salary, position)


ws = WorkingStudent("john", "brown", 18, 1, [1, 2, 3], 1000, 'Programmer')
print(ws)
print(ws.name)
print(ws.age)

你的输出将是...

输出：

<main.WorkingStudent object at 0x7fc6c4d8ba10>
john
18
[1, 2, 3]

如何创建多个继承class的实例？

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