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
