c3算法和 mro super用法

Posted 2021-01-23 liurenli

# super()# MRO + super ?面试题

# super是查找mro顺序中的下一个
# 单继承中我们可以认为super是对父类中的属性或方法的引入

class ShengWu:
    def dong(self):  # 实例方法
        print(self)
        print("我是生物")


class Animal(ShengWu):
    pass


class Cat(Animal):
    def dong(self):  # 子类中出现了和父类重名的内容. 表示对父类的方法的覆盖(重写). 半盖(java)
        super(Animal, self).dong()  # 定位到Animal. 找Animal的下一个
        # super(类, 对象).方法()  找到MRO中的类. 找这个类的下一个. 去执行方法
        print("我的猫也会动")


# 找MRO中的下一个
# Cat -> Animal -> ShengWu

c = Cat()
print(c)
c.dong()


# MRO + super ?试题
class Init(object):
    def __init__(self, v):
        print("init")
        self.val = v  # 2


class Add2(Init):
    def __init__(self, val):  # 2
        print("Add2")
        super(Add2, self).__init__(val)
        print(self.val)  # 5.0
        self.val += 2  # 7.0


class Mult(Init):
    def __init__(self, val):
        print("Mult")
        super(Mult, self).__init__(val)
        self.val *= 5  # 5.0


class HaHa(Init):
    def __init__(self, val):
        print("哈哈")
        super(HaHa, self).__init__(val)
        self.val /= 5  # 1.0


class Pro(Add2, Mult, HaHa):  #
    pass


class Incr(Pro):
    def __init__(self, val):  # 5
        super(Incr, self).__init__(val)
        self.val += 1  # 8.0

        ‘‘‘
        add2
        Mult
        哈哈
        init
        5.0
        8.0
        Add2
        init
        2
        4

        ‘‘‘


# Incr, pro, add2, mult, haha, Init
p = Incr(5)
print(p.val)  # ?
# Add2 init
c = Add2(2)
print(c.val)  # ?


# ------------------------------------------------------------------------------------------------------------#
# 新式类的MRO(重点, 难点) C3算法
#         先拆分
#         再合并 第一项的头和后面所有项的尾进行比较如果出现了. 就拿出来 如果没出现. 下一项....


class A:
    pass
class B(A):
    pass
class C(A):
    pass
class D(B, C):
    pass
class E(C, A):
    pass
class F(D, E):
    pass
class M(F, E):
    pass
class N:
    pass
class P(M,N):
    pass
class G(P):
    pass
class O:
    pass
class X(O):
    pass
class H(G, X, F):
    pass
print(H.__mro__)
‘‘‘
L(H) = H + L(G) + L(X) + L(F) + GXF   HGPMXFDBECANO

L(G) = G + L(P)  + P          # GPMFDBECAN
L(X) = X + L(O) + O           # XO 
L(F) = F + L(D) + L(E) + DE   #   FDBECA


L(P) = P + L(M) + L(N) + MN   #  PMFDBECAN
L(D) = D + L(B) + L(C) + BC   #    DBCA
L(E) = E + L(C) + L(A) + CA   #    ECA

L(M) = M + L(F) + L(E) + FE   # ECA   ECA E    MFDBECA

‘‘‘


‘‘‘
L(H) = H + L(G) + X+ L(F)        HGPMFDBECAN FDBECA

L(G) = G + L(P)  GPMFDBECAN
L(F) = F + L(D) + L(E)  FDBECA

L(P) = P + L(M) + L(N)  PMFDBECAN
L(D) = D + L(B) + L(C)  DBCA
L(E) = E + L(C) + L(A)  ECA

L(M) = M + L(F) + L(E)  MFDBECA
L(N) = N
L(B) = B + L(A)   BA
L(C) = C + L(A)   CA

L(A) = A
‘‘‘


‘‘‘
设L为查找方法的MRO顺序
L(H) = H + L(G) + L(F)
L(G) = G + L(E)
L(F) = F + L(D) + L(E)
L(D) = D + L(B) + L(C)
L(B) = B + L(A)
L(E) = E + L(C) + L(A)
L(C) = C + L(A)
L(A) = A


合并. 从下向上合并. 拿出每一项的头和后一项的身体进行比较. 如果出现了. 就过, 从后一项的头继续去比较. 如果不出现就出来

HGFDBECA

L(H) = H + L(G) + L(F)   ECA + FDBECA   
L(G) = G + L(E)  GECA
L(F) = F + L(D) + L(E)   FDBECA
L(D) = D + L(B) + L(C)   DBCA
L(B) = B + L(A)            BA
L(E) = E + L(C) + L(A)    ECA
L(C) = C + A   CA
L(A) = A

新式类通过__mro__可以直接看到MRO的结果
‘‘‘
# HGF   DBE    CA  object
# print(H.__mro__)

# 给面试官用的