Python 类继承

Question

我在理解 python 的 mro（方法解析顺序）时遇到了一些麻烦。 Python 从左到右运行。因此，根据我的理解，调用 M 的顺序应该是。 M、B、A、Z、X、Y

class X: pass
class Y: pass
class Z: pass

class A(X,Y): pass
class B(Y,Z): pass

class M(B,A,Z): pass

print(M.mro())

但是正确的调用顺序是。

    [<class '__main__.M'>,
 <class '__main__.B'>,
 <class '__main__.A'>,
 <class '__main__.X'>,
 <class '__main__.Y'>,
 <class '__main__.Z'>,
 <class 'object'>]

谁能解释一下顺序并帮助我理解这一点。谢谢

Answer 1

mro 从 Python2.3 开始就基于 C3 算法，“合并”是该算法的核心。 how merge works。 根据你的代码，这里我们可以列出如何获取mro(M)：

mro(M) = [M] + merge(mro(B), mro(A), mro(Z), [B,A,Z])    

mro(B) = [B] + merge(mro(Y) , mro(Z)) = [B] + merge([Y] , [Z])
       = [B,Y] + merge([Z]) 
       = [B,Y,Z]

mro(A) = [A] + merge(mro(X) , mro(Y)) 
       = [A] + merge([X],[Y]) 
       = [A,X,Y]

mro(Z) = [Z]

返回mro(M):

mro(M) = [M] + merge([B,Y,Z), [A,X,Y], [Z], [B,A,Z]) 
       = [M,B] + merge([Y,Z], [A,X,Y], [Z], [A,Z]) 
       = [M,B,A] + merge([Y,Z], [X,Y], [Z], [Z]) 
       = [M,B,A,X] + merge([Y,Z] + [Y] + [Z], [Z]) 
       = [M,B,A,X,Y] + merge([Z] + [Z] + [Z]) 
       = [M,B,A,X,Y,Z]