python多重继承:避免以菱形形式调用构造函数两次
考虑以下代码:python多重继承:避免以菱形形式调用构造函数两次,python,initialization,multiple-inheritance,super,diamond-problem,Python,Initialization,Multiple Inheritance,Super,Diamond Problem,考虑以下代码: class A(object): def __init__(self): print("A.__init__") super(A, self).__init__() # 1 print("A.__init__ finished") class B(A): def __init__(self): print("B.__init__") super(B, self)._
class A(object):
def __init__(self):
print("A.__init__")
super(A, self).__init__() # 1
print("A.__init__ finished")
class B(A):
def __init__(self):
print("B.__init__")
super(B, self).__init__() # 2
print("B.__init__ finished")
class C(A):
def __init__(self):
print("C.__init__")
super(C, self).__init__()
print("C.__init__ finished")
class D(B, C):
def __init__(self):
print("D.__init__")
print("Initializing B")
B.__init__(self) # 3
print("B initialized")
print("Initializing C")
C.__init__(self) # 4
print("C initialized")
print("D.__init__ finished")
D()
# D.__init__
# Initializing B
# B.__init__
# C.__init__
# A.__init__
# A.__init__ finished
# C.__init__ finished
# B.__init__ finished
# B initialized
# Initializing C
# C.__init__
# A.__init__
# A.__init__ finished
# C.__init__ finished
# C initialized
# D.__init__ finished
据我了解,算法如下:
D.__init__ at (3) -> B.__init__ ->
-> super().__init__ -> (super of self.__class__).__init__ ->
-> C.__init__ (# why C?) -> super().__init__ ->
-> A.__init__
D.__init__ at (4) -> C.__init__ ->
-> super().__init__ ->
-> A.__init__
实际上有三个问题:1.为什么
super()
2.在这种情况下,如何避免调用C.\uuuuu init\uuuu
和A.\uuuuu init\uuuuu
两次?
2.1初始化当前类继承自的所有类的正确方法是什么?Q:为什么super()。\uuuu init\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu()
在B中调用
当你打电话的时候
super(X, self).__init__
Python查找self.\uuu类\uuuu.mro()
。然后,它从MRO中X之后的下一个类调用\uuuuu init\uuuu
当self是D
的实例时,self.\uuu class\uuuu.mro()
是[D,B,C,A]
。所以super(B,self).\uuu init\uuu()
调用C.\uu init\uuuu(self)
Q:初始化当前类继承自的所有类的正确方法是什么
在D.\uuuuu init\uuuuu
中也使用super:
class D(B, C):
def __init__(self):
print("D.__init__")
super(D, self).__init__()
print("D.__init__ finished")
问:当self是D的一个实例时,为什么要调用super()。\uuuuu init\uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu
当你打电话的时候
super(X, self).__init__
Python查找self.\uuu类\uuuu.mro()
。然后,它从MRO中X之后的下一个类调用\uuuuu init\uuuu
当self是D
的实例时,self.\uuu class\uuuu.mro()
是[D,B,C,A]
。所以super(B,self).\uuu init\uuu()
调用C.\uu init\uuuu(self)
Q:初始化当前类继承自的所有类的正确方法是什么
在D.\uuuuu init\uuuuu
中也使用super:
class D(B, C):
def __init__(self):
print("D.__init__")
super(D, self).__init__()
print("D.__init__ finished")
我贴了一个简化的箱子。实际的B类和C类有不同的签名。这是使用super的一种方法。签名必须全部匹配,因为您无法控制超级用户接下来调用哪个类的方法。为了平衡文章中的陷阱,也请阅读。我发布了一个简化的案例。实际的B类和C类有不同的签名。这是使用super的一种方法。签名必须全部匹配,因为您无法控制超级用户接下来调用哪个类的方法。为了平衡文章中的陷阱,也请阅读。