巨蟒python全栈开发-第21天继承

一.今日主要内容

1.了解python2和python3类的区别
    python2在2.2之前使用的是经典类,2.2之后,使用的是新式类
    class Foo:
        pass
    class Foo(object):
        pass

    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递归遍历,这个需要了解)=>树形结构的遍历

3.新式类的MRO C3算法(笔试或者面试别人的算法)(难点,重点)(python没有用过广度优先)
    (1)拆分
    (2)合并

    用头和身体比较
4.super() 找MRO顺序的下一个    #只有讲完MRO才能讲
5.一道面试题

二.今日内容大纲:

1.深度递归

2.MRO_C3

3.super

三.今日内容详解:

1.深度递归

class A:

    pass

class B(A):

    pass

class C(A):

    pass

class D(B, C):

    pass

class E:

    pass

class F(D, E):

    pass

class G(F, D):

    pass

class I:

    pass

class J(B, C):

    pass

class K(A):

    pass

class H(I, J, K):

    pass

class Foo(H, G):

    pass

结果:

#FOO=>H=>I=>J=>B=>A=>C=>K=>G=>F=>D=>E

2.MRO_C3

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     (Q+PECA+NM+X+PNX)

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__)

3.super

(1)

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')

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

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

        #super(Base1,self).chi()

        #super(Base2,self).chi()

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

b.chi()

print(Bar.__mro__)

(2)

class Base1:

    def chi(self):

        super().chi() # super找的是MRO的下一个.

        print("我是可怜的Base1")

class Base2:

    def chi(self):

        super().chi()

        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(Bar, 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() # 报错 如果是Base1 object,会报错,注意这里的细节

b.chi() # 报错

# 坑

(3)

# MRO + super ⾯试题

class Init(object):                        #在下面对应子类和父类都可以

    def __init__(self,v):                  #在这里注意解题的标记

        print('init')                           #HaHa

        self.val=v

class Add2(Init):

    def __init__(self,val):

        print('Add2')

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

        print(self.val)

        self.val+=2

class Mult(Init):

    def __init__(self,val):

        print('Mult')

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

        self.val*=5

class HaHa(Init):

    def __init__(self,val):

        print('哈哈')

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

        self.val/=5

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

    pass

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

    def __init__(self,val):

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

        self.val+=1

# print(Incr.__mro__)

p=Incr(5)

print(p.val)

# Incr Pro Add2 Mult HaHa Init

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

'''结果:

# # Add2

# # Mult

# # 哈哈

# # init

# # 5.0

# # 8.0

'''

p=Add2(2)

print(p.val)

# Add2, Init, Object c.val = 2

# Add2

# init

#

#

'''

MRO: method resolution order            #方法查找顺序

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

'''

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