Python：如何使用super（）初始化2个超类？

Question

我有两个超级班，父亲和母亲，他们将由Child继承。

class Father:
  def __init__(self, **kwargs):
    self.fathername = kwargs["ffn"] + " " + kwargs["fln"]
    self.fatherage = kwargs["fa"]

class Mother:
  def __init__(self, **kwargs):
    self.mothername = kwargs["mfn"] + " " + kwargs["mln"]
    self.motherage = kwargs["ma"]

这里的班级继承父亲和母亲

class Child(Father, Mother):
  def __init__(self, **kwargs):
    self.name = kwargs["name"] + " " + kwargs["lastname"]
    self.age = kwargs["age"]

如果我分别打电话给他们的__init__()s，我可以初始化父亲和母亲。

    Father.__init__(self, **kwargs)
    Mother.__init__(self, **kwargs)

但是如何用super（）实现相同的目标呢？如果我把它称为下面，它只会初始化父亲而不是母亲（因为父亲是我认为的MRO中的下一个）

    super().__init__(**kwargs)

下面是__str__()被覆盖以显示分配的内容。

def __str__(self):
    return \
    "Im {}, {} years old".format(self.name, self.age) + "\n" + \
    "My dad is {} and he is {} years old".format(self.fathername, self.fatherage) + "\n" + \
    "My mom is {} and she is {} years old".format(self.mothername, self.motherage)

familyname = "Simpson"
child = Child(**{"name": "Bart", "lastname": familyname, "age": 15, "ffn": "Hommer", "fln": familyname, "fa": 54, "mfn": "Marggie", "mln": familyname, "ma": 46})

当我尝试打印对象时，它将失败，因为母亲超类从未被初始化（当我在儿童super()中使用__init__()时）

print(child)

The program raises a runtime error

Traceback (most recent call last):
  File "/tmp/pyadv.py", line 225, in <module>
    print(child)
  File "/tmp/pyadv.py", line 217, in __str__
    return     "Im {}, {} years old".format(self.name, self.age) + "\n" +     "My dad is {} and he is {} years old".format(self.fathername, self.fatherage) + "\n" +     "My mom is {} and she is {} years old".format(self.mothername, self.motherage)
AttributeError: 'Child' object has no attribute 'mothername'

那么，我如何使用super来初始化两个超类呢？

编辑：我试图将super(Father, self).__init__(**kwargs)和super(Mother, self).__init__(**kwargs)添加到超类__init__()方法但我得到以下错误：

Traceback (most recent call last):
  File "/tmp/pyadv.py", line 225, in <module>
    child = Child(**{"name": "Bart", "lastname": familyname, "age": 15, "ffn": "Hommer", "fln": familyname, "fa": 54, "mfn": "Marggie", "mln": familyname, "ma": 46})
  File "/tmp/pyadv.py", line 217, in __init__
    super().__init__(**kwargs)
  File "/tmp/pyadv.py", line 199, in __init__
    super(Father, self).__init__(**kwargs)
  File "/tmp/pyadv.py", line 208, in __init__
    super(Mother, self).__init__(**kwargs)
TypeError: object.__init__() takes no parameters

我还尝试将super(Father, self).__init__()和super(Mother, self).__init__()（__init__()中没有参数）添加到超类__init__()方法，但我得到以下错误：

Traceback (most recent call last):
  File "/tmp/pyadv.py", line 225, in <module>
    child = Child(**{"name": "Bart", "lastname": familyname, "age": 15, "ffn": "Hommer", "fln": familyname, "fa": 54, "mfn": "Marggie", "mln": familyname, "ma": 46})
  File "/tmp/pyadv.py", line 217, in __init__
    super().__init__(**kwargs)
  File "/tmp/pyadv.py", line 199, in __init__
    super(Father, self).__init__()
  File "/tmp/pyadv.py", line 206, in __init__
    self.mothername = kwargs["mfn"] + " " + kwargs["mln"]
KeyError: 'mfn'

解决方案1：@blkkngt在下面剥离

解决方案2：根超类，详细的here。

class Root:
  def __init__(self, **kwargs):
    pass

class Father(Root):
  def __init__(self, **kwargs):
    self.fathername = kwargs["ffn"] + " " + kwargs["fln"]
    self.fatherage = kwargs["fa"]
    super().__init__(**kwargs)

class Mother(Root):
  def __init__(self, **kwargs):
    self.mothername = kwargs["mfn"] + " " + kwargs["mln"]
    self.motherage = kwargs["ma"]
    super().__init__(**kwargs)

class Child(Father, Mother):
  def __init__(self, **kwargs):
    self.name = kwargs["name"] + " " + kwargs["lastname"]
    self.age = kwargs["age"]
    super().__init__(**kwargs)
  def __str__(self):
    return \
    "Im {}, {} years old".format(self.name, self.age) + "\n" + \
    "My dad is {} and he is {} years old".format(self.fathername, self.fatherage) + "\n" + \
    "My mom is {} and she is {} years old".format(self.mothername, self.motherage)

familyname = "Simpson"
child = Child(**{"name": "Bart", "lastname": familyname, "age": 15, "ffn": "Homer", "fln": familyname, "fa": 54, "mfn": "Marge", "mln": familyname, "ma": 46})

print(child)

Answer 1

Python中的多重继承需要合作。也就是说，两个父类需要知道彼此存在的可能性（尽管他们不需要知道彼此的任何细节）。然后，无论哪个父亲首先被命名，都可以调用另一个父母的__init__方法。这就是super的工作原理，它总是调用正在操作的实例的MRO中的下一个类（方法解析顺序）。

您的代码很难正确执行此操作，因为您总是在kwargs调用中传递完整的super字典。当第二个父亲试图调用MRO中的最后一个类object时，这会成为一个问题，因为它不期望接收任何关键字参数。相反，每个类的__init__方法通常应该明确地命名它所期望的参数，而不是在调用super().__init__时再次传递它们（除非它知道它的一个父类也需要参数）。

试试这个：

class Father:
  def __init__(self, ffn, fln, fa, **kwargs): # name the parameters we expect
    super().__init__(**kwargs)           # pass on any unknown arguments
    self.fathername = ffn + " " + fln    # use parameters by name, rather than via kwargs
    self.fatherage = fa

class Mother:
  def __init__(self, mfn, mln, ma, **kwargs):
    super().__init__(**kwargs)
    self.mothername = mfn + " " + mln
    self.motherage = ma

class Child(Father, Mother):
  def __init__(self, name, lastname, age, **kwargs):
    super().__init__(**kwargs)
    self.name = name " " + lastname
    self.age = age

    def __str__(self):
        return \
        "Im {}, {} years old".format(self.name, self.age) + "\n" + \
        "My dad is {} and he is {} years old".format(self.fathername, self.fatherage) + "\n" + \
        "My mom is {} and she is {} years old".format(self.mothername, self.motherage)


familyname = "Simpson"
child = Child(name="Bart", lastname=familyname, age=15, # you can use keyword syntax here
              ffn="Homer", fln=familyname, fa=54,
              mfn="Marge", mln=familyname, ma=46)
print(child)

请注意，在Python 3中，您通常不需要将任何参数传递给super()，它可以确定从哪个类调用并自动工作。在Python 2中，您必须指定当前类，但不再需要它。

最后一点。虽然我确信您的代码只是一个示例，但在OOP设计方面，类的名称非常差。继承意味着两个类之间的IS-A关系，这对人们来说并不合适。例如，在示例代码中创建的子代（Bart）不是Mother或Father，但代码说他是，因为他是Mother和Father类的实例。描述与父母的人际关系的更好方法是HAS-A。每个孩子都有一位母亲和一位父亲。您可以使用封装来建立HAS-A关系。这意味着，子对象将引用属性中每个父对象的对象。有趣的是，这可以只用一个类来完成（这可能就是为什么你没有学习这个，如果你正在学习继承）：

class Person:
    def __init__(self, firstname, lastname, age, father=None, mother=None):
        self.name = firstname + " " + lastname
        self.age = age
        self.father = father  #  set the attributes for our parents here
        self.mother = mother

fn = "Simpson"
bart = Person("Bart", fn, 15, Person("Homer", fn, 54), Person("Marge", fn, 46))

Answer 2

从这个link接受的答案：

通过super调用不会调用所有父项，它调用MRO链中的下一个函数。为了使其正常工作，您需要在所有__init__s中使用super

class Parent1(object):
    def __init__(self):
        super(Parent1, self).__init__()
        self.var1 = 1

class Parent2(object):
    def __init__(self):
        super(Parent2, self).__init__()
        self.var2 = 2

class Child(Parent1, Parent2):
    def __init__(self):
        super(Child, self).__init__()