面向对象的进阶

item系列方法

通过item方法，可以实现像字典一样操作对象

class Foo:
    def __init__(self,name,age,sex):
        self.name=name
        self.age = age
        self.sex = sex
    def __getitem__(self, item):
        return self.__dict__[item]

    def __setitem__(self, key, value):
        self.__dict__[key]=value

    def __delitem__(self, key):
        del self.__dict__[key]

f=Foo('tom',24,'男')
print(f['name'])#可以实现像字典一样取值
f['hobby']='男'
print(f.hobby,f['hobby'])
del f.hobby#这种方法是object原生支持，其实内部运行的是__delattr__
del f['hobby']#和__delitem__配合删除了f['hobby'],这是通过delitem配合实现
print(f.__dict__)

new

__init__初始化方法
__new__构造方法，创建一个方法

class A:
    def __init__(self):
        self.x=1
        print('in init function')
    def __new__(cls,*args,**kwargs):
        print('in new function')
        return object.__new__(A,*args, **kwargs)#代码先执行到这里，此时还没有self,所以这里用了object
a=A()

D:\anoconda\python.exe F:/python/python学习/人工智能/第一阶段day2/3.二分查找算法.py
in new function
in init function

Process finished with exit code 0

 

单例模式：
一个类始终只有一个实例。当第一次实例化这个对象的时候，就创建一个实例化对象
当之后再来实例化的时候，就用之前创建的对象。也就是说实例不变，变化的只是对象

class A:
    __isinstance=False
    def __init__(self,name,age):
        self.name=name
        self.age = age
    def __new__(cls,*args,**kwargs):
        if cls.__isinstance:
            return cls.__isinstance
        cls.__isinstance=object.__new__(A)
        return cls.__isinstance

Jack=A('jack',24)
Jack.cloth='red'

Tom=A('tom',24)
print(Jack)
print(Tom)
print(Jack.name)
print(Tom.name)
print(Jack.cloth)

 

__eq__

class A:
    def __init__(self,name):
        self.name=name

ob1=A('egg')
ob2=A('egg')
print(ob1==ob2)#虽然ob1和ob2内容相同，但是计算机是根据内存地址判断，两个的内存地址不一样，所以结果肯定是false

加上__eq__方法后，结果为true

class A:
    def __init__(self,name):
        self.name=name
    def __eq__(self, other):
        if self.name==other.name:
            return True
        else:
            return False
ob1=A('egg')
ob2=A('egg')
print(ob1==ob2)

__hash__

class A:
    def __init__(self,name,sex):
        self.name=name
        self.sex=sex
    def __hash__(self):
        return hash(self.name+self.sex)
a=A('egg','男')
b=A('egg','男')
print(hash(a))
print(hash(b))#结果完全相同

D:\anoconda\python.exe F:/python/python学习/人工智能/第一阶段day2/3.二分查找算法.py
8412774350429136977
8412774350429136977

Process finished with exit code 0

加上__hash__

class A:
    def __init__(self,name):
        self.name=name
a=A('egg')
b=A('egg')
print(hash(a))
print(hash(b))#结果完全不同
D:\anoconda\python.exe F:/python/python学习/人工智能/第一阶段day2/3.二分查找算法.py
-9223371863945030947
172909893033

Process finished with exit code 0

利用面向对象的内置方法实现纸牌游戏：

import json
from collections import namedtuple
Card=namedtuple('Card',['rank','suit'])
class FranchDeck:
    ranks=[str(n) for n in range(2,11)]+list('JQKA')
    suits=['红心','方块','梅花','黑桃']
    def __init__(self):
        self._cards=[Card(rank,suit) for rank in FranchDeck.ranks
                                    for suit in FranchDeck.suits]
    def __len__(self):
        return len(self._cards)

    def __getitem__(self, item):
        return self._cards[item]

    def __setitem__(self, key, value):
        self._cards[key]=value

    def __str__(self):
        return json.dumps(self._cards,ensure_ascii=False)

deck=FranchDeck()
print(deck[0])
from random import choice
print(choice(deck))#这里实现了随机抽牌
from random import shuffle#这里实现了洗牌
shuffle(deck)
print(deck[10])
print(deck)

题目：数据库中的人名和性别不变，随着年数的增长，年龄逐渐增长

class A:
    def __init__(self,name,sex,age):
        self.name=name
        self.sex = sex
        self.age=age
    def __hash__(self):
        return hash(self.name+self.sex)

a=A('egg','男',18)
b=A('egg','男',17)
print(set((a,b)))

D:\anoconda\python.exe F:/python/python学习/人工智能/第一阶段day2/3.二分查找算法.py
{<__main__.A object at 0x000001E030115B00>, <__main__.A object at 0x000001E030115BE0>}

Process finished with exit code 0

可见，单纯使用hash值无法解决问题

class A:
    def __init__(self,name,sex,age):
        self.name=name
        self.sex = sex
        self.age=age
    def __eq__(self, other):
        if self.name==other.name and self.sex==other.sex:
            return True
        return False
    def __hash__(self):
        return hash(self.name+self.sex)

a=A('egg','男',18)
b=A('egg','男',17)
print(set((a,b)))

D:\anoconda\python.exe F:/python/python学习/人工智能/第一阶段day2/3.二分查找算法.py
{<__main__.A object at 0x00000211D31F5B38>}

Process finished with exit code 0