day 21继承

1.了解Python2和python3类的区别:

  python2.3之前使用的是经典类, 在2.3版本之后组,使用的是新式类

MRO: method resolution order  方法的查找顺序

MRO: method resolution order 方法的查找顺序

 

        class Base:

            pass

 

        class Base1:

            def chi():

                pass

 

        class Bar(Base, Base1):

            pass

 

        b = Bar() # Bar -> Base -> Base1

        b.chi()

2.经典类的MRO  树形结构的深度优先遍历   -> 树形结构遍历

注意:新式类的不是广度的遍历

3.新式类的MRO  c3算法(重点,难点)

    1.拆分

     2.合并

用头和身体进行比较,如果头在身子里面存在,取身子的头,如果头在身子里面不存在,取头

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:

    pass

class N(M):

    pass

class P(E, A):

    pass

class X:

    pass

class Q(P,N,X):

    pass

class G(Q, F):

    pass

class H(G, F):

    pass

 

'''

L(H) = H + L(G) + L(F) + GF # HGQPFDBECANMX

L(G) = G + L(Q) + L(F) + QF # GQPFDBECANMX

L(Q) = Q + L(P) + L(N) + X + PNX # QPECANMX

L(P) = P + L(E) + A + EA  # PECA

L(E) = E + L(C) + A + CA   # ECA

L(C) = C + A + A   # CA

L(N) = N + M # NM

 

L(F) = F + L(D) + L(E) + DE # FDBECA

L(D) = D + L(B) + L(C) + BC # DBCA

 

 

'''

 

'''

    求H的MRO

    设求MRO的算法是L

    L(H) = H + L(G) + L(F) + GF

    L(G) = G + L(E) + E

    L(E) = E + L(C) + L(A) + CA

    L(C) = C + L(A) + A

    L(A) = A

    L(F) = F + L(D) + L(E) + DE

    L(D) = D + L(B) + L(C) + BC

    L(B) = B + L(A) + A

 

    # 加法:merge(), 拿第一项的第一位和 后面每项的除了第一位比较. 如果没有出现, 则该位元素算出

        如果出现了. 此时开始下一项的第一位继续和后面每一项的除了第一位比较:

        

        用头和后面身体比较

            

    L(H) = H + L(G) + L(F) + GF # ECA + DBECA  = HGFDBECAO

    L(G) = G + L(E) + E # GECA

    L(E) = E + L(C) + L(A) + CA # ECA

    L(C) = C + L(A) + A  # CA

    L(A) = A

    L(F) = F + L(D) + L(E) + DE # FDBECA

    L(D) = D + L(B) + L(C) + BC # DBCA

    L(B) = B + A + A   # BA

'''

print(H.__mro__)

4.super() 找MRO顺序的下一个

class Base1:

    def chi(self):

        print("我是可怜的Base1")

 

class Base2:

    def chi(self):

        print("我是可怜的Base2")

 

class Base3:

    def chi(self):

        print("我是可怜的Base3")

 

class Bar(Base1, Base2, Base3):

    def chi(self):

        print("我是Bar里面的吃1")

        # super(类名, self) 从某个类开始找下一个MRO

        super(Base2, self).chi() # 此时调用的super. 在Bar调用 -> super表示找MRO里的下一个

        # super().chi() # super(Bar, self).chi()

        print("我是Bar里面的吃2")

 

b = Bar() # Bar, Base1, Base2, Base3, object   顺序

b.chi()

print(Bar.__mro__)

5.一道面试题

# MRO + super ⾯试题

class Init(object):

    def __init__(self, v): # 2

        print("init")

        self.val = v

 

class Add2(Init):

    def __init__(self, val): # 2

        print("Add2")

        super(Add2, self).__init__(val) # Mult

        print(self.val)

        self.val += 2

 

class Mult(Init):

    def __init__(self, val):

        print("Mult")

        super(Mult, self).__init__(val) # Haha

        self.val *= 5

 

class HaHa(Init):

   def __init__(self, val):

        print("哈哈")

        super(HaHa, self).__init__(val) # Init

        self.val /= 5

 

class Pro(Add2,Mult,HaHa): #

    pass

 

class Incr(Pro): # incr->pro->add2->Mult->HaHa->init

    def __init__(self, val): # 5

        super(Incr, self).__init__(val) # Add2

        self.val += 1

 

 

 

'''

MRO: method resolution order

Incr,Pro,Add2,Mult,HaHa,Init,Object

 

super()

a = Incr()

a.chi()

'''

 

# print(Incr.__mro__)

# Incr Pro Add2 Mult HaHa Init

p = Incr(5) # p.val = 8.0

# Add2

# Mult

# 哈哈

# init

# 5.0

# 8.0

print(p.val)

 

c = Add2(2) # Add2, Init, Object c.val = 2

# Add2

# init

# 2

# 4

 

print(c.val) # 4