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
# 2
# 4
'''
MRO: method resolution order #方法查找顺序
Incr,Pro,Add2,Mult,HaHa,Init,Object
'''