python基础(14)-反射&类的内置函数

反射

几个反射相关的函数可参考python基础(10)-匿名函数&内置函数中2.2.4反射相关

类的一些内置函数

__str__()&__repr__()

重写__str__()函数类似重写java中的toString()函数.当没有重写__str__()但重写了__repr__()函数时,__repr__()函数会充当一个__str__函数的替代函数执行

 class Person1:
     def __init__(self, name, age):
         self.name = name
         self.age = age

     def __str__(self):
         return "name:{} age:{}".format(self.name, self.age)

 p1 = Person1('张三', 18)
 print(p1)  # name:张三 age:18

 class Person2:
     def __init__(self, name, age):
         self.name = name
         self.age = age

     def __repr__(self):
         return "name:{} age:{}".format(self.name, self.age)

 p2 = Person2('张三', 18)
 print(p1)  # name:张三 age:18

__del__()

销毁一个对象的时候执行,类似java中的析构函数

 class A:
     def __del__(self):
         print("from del")

 a = A()
 del a  # from del

__getitem__()&__setitem__()&__delitem__()

以'[]'的形式访问属性

 class Person:
     def __init__(self, name, age):
         self.name = name
         self.age = age

     def __getitem__(self, item):
         print("from __getitem__:{}".format(item))
         return self.__dict__[item]

     def __setitem__(self, key, value):
         print("from __setitem__:{} = {}".format(key, value))
         self.__dict__[key] = value

     def __delitem__(self, key):
         print("from __delitem__:{}".format(key))

 p = Person('张三', 18)
 name = p['name']  # from __getitem__:name
 print(name)  # 张三

 p['age'] = 20  # from __setitem__:age = 20

 # 和@property.deleter相似 del时只是触发对应方法 并不是真的删除
 del p['age']  # from __delitem__:age
 

__new__()

创建对象(self),类似java中的构造函数,在__init__()函数之前执行

 class Person:
     def __init__(self, name, age):
         print('from __init__()')
         self.name = name
         self.age = age

     def __new__(cls, *args, **kwargs):
         print('from __new__()')
         return object.__new__(cls)

 p = Person('张三', 18)

 # result:
 # from __new__()
 # from __init__()

__call__()

让一个类的实例成为一个callable对象

 class Person:
     def __init__(self, name, age):
         self.name = name
         self.age = age

     def __call__(self, *args, **kwargs):
         print('name:{} age:{}'.format(self.name, self.age))

 p = Person('张三', 18)
 print(callable(p))  # True
 p()  # name:张三 age:18

__len__()

对len()函数传入一个对象实际上就是调用这个对象的__len__()函数

 class Person:
     def __init__(self, name, age):
         self.name = name
         self.age = age

     def __len__(self):
         return len(self.name)

__hash__()

对hash()函数传入一个对象实际上就是调用这个对象的__hash__()函数

 class Person:
     def __init__(self, no, name, age):
         self.no = no
         self.name = name
         self.age = age

     def __hash__(self):
         return self.no

 p = Person(1, '张三', 18)
 

__eq__()

使用'=='判断两个对象是否相等时,依据__eq__()函数返回的值.类似java中的equals()函数

 class Person:
     def __init__(self, name, age):
         self.name = name
         self.age = age

     def __eq__(self, other):
         return self.name == other.name

 p1 = Person('张三', 19)
 p2 = Person('张三', 18)
 print(p1 == p2)  # True

扩展

单例模式

 class Single:
     instance = None

     def __new__(cls, *args, **kwargs):
         if cls.instance:
             return cls.instance
         cls.instance = object.__new__(cls)
         return cls.instance

 o1 = Single()
 o2 = Single()
 print(o1)  # <__main__.Single object at 0x00000000021EDAC8>
 print(o2)  # <__main__.Single object at 0x00000000021EDAC8>

扑克牌

 from collections import namedtuple
 from random import choice, shuffle

 CardTuple = namedtuple('Card', ['suit', 'rank'])

 class Card:
     def __init__(self):
         suit_list = ['红桃', '黑桃', '梅花', '方块']
         rank_list = [str(i) for i in range(2, 11)] + ['J', 'Q', 'K', 'A']
         self.card_list = [CardTuple(suit, rank) for rank in rank_list for suit in suit_list]

     def __str__(self):
         return str(self.card_list)

     def __len__(self):
         return len(self.card_list)

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

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

 # 一幅扑克牌
 card = Card()
 print(
     card)  # [Card(suit='红桃', rank='2'), Card(suit='黑桃', rank='2'), Card(suit='梅花', rank='2'), Card(suit='方块', rank='2'), Card(suit='红桃', rank='3'), Card(suit='黑桃', rank='3'), Card(suit='梅花', rank='3'), Card(suit='方块', rank='3'), Card(suit='红桃', rank='4'), Card(suit='黑桃', rank='4'), Card(suit='梅花', rank='4'), Card(suit='方块', rank='4'), Card(suit='红桃', rank='5'), Card(suit='黑桃', rank='5'), Card(suit='梅花', rank='5'), Card(suit='方块', rank='5'), Card(suit='红桃', rank='6'), Card(suit='黑桃', rank='6'), Card(suit='梅花', rank='6'), Card(suit='方块', rank='6'), Card(suit='红桃', rank='7'), Card(suit='黑桃', rank='7'), Card(suit='梅花', rank='7'), Card(suit='方块', rank='7'), Card(suit='红桃', rank='8'), Card(suit='黑桃', rank='8'), Card(suit='梅花', rank='8'), Card(suit='方块', rank='8'), Card(suit='红桃', rank='9'), Card(suit='黑桃', rank='9'), Card(suit='梅花', rank='9'), Card(suit='方块', rank='9'), Card(suit='红桃', rank='10'), Card(suit='黑桃', rank='10'), Card(suit='梅花', rank='10'), Card(suit='方块', rank='10'), Card(suit='红桃', rank='J'), Card(suit='黑桃', rank='J'), Card(suit='梅花', rank='J'), Card(suit='方块', rank='J'), Card(suit='红桃', rank='Q'), Card(suit='黑桃', rank='Q'), Card(suit='梅花', rank='Q'), Card(suit='方块', rank='Q'), Card(suit='红桃', rank='K'), Card(suit='黑桃', rank='K'), Card(suit='梅花', rank='K'), Card(suit='方块', rank='K'), Card(suit='红桃', rank='A'), Card(suit='黑桃', rank='A'), Card(suit='梅花', rank='A'), Card(suit='方块', rank='A')]
 # 扑克牌张数

 # 取第十张
 print(card[10 - 1])  # Card(suit='黑桃', rank='4')
 # 随机抽取一张
 print(choice(card))  # Card(suit='方块', rank='7')
 # 洗牌
 shuffle(card)
 print(
     card)  # [Card(suit='黑桃', rank='8'), Card(suit='梅花', rank='6'), Card(suit='黑桃', rank='2'), Card(suit='红桃', rank='4'), Card(suit='梅花', rank='4'), Card(suit='红桃', rank='K'), Card(suit='方块', rank='9'), Card(suit='梅花', rank='7'), Card(suit='梅花', rank='9'), Card(suit='方块', rank='4'), Card(suit='红桃', rank='7'), Card(suit='黑桃', rank='J'), Card(suit='红桃', rank='8'), Card(suit='梅花', rank='K'), Card(suit='红桃', rank='J'), Card(suit='黑桃', rank='6'), Card(suit='红桃', rank='A'), Card(suit='红桃', rank='10'), Card(suit='梅花', rank='5'), Card(suit='方块', rank='6'), Card(suit='方块', rank='10'), Card(suit='方块', rank='8'), Card(suit='方块', rank='7'), Card(suit='黑桃', rank='Q'), Card(suit='方块', rank='A'), Card(suit='红桃', rank='6'), Card(suit='梅花', rank='8'), Card(suit='梅花', rank='J'), Card(suit='梅花', rank='3'), Card(suit='方块', rank='J'), Card(suit='方块', rank='5'), Card(suit='梅花', rank='2'), Card(suit='黑桃', rank='4'), Card(suit='梅花', rank='A'), Card(suit='黑桃', rank='3'), Card(suit='黑桃', rank='5'), Card(suit='方块', rank='K'), Card(suit='红桃', rank='Q'), Card(suit='方块', rank='3'), Card(suit='方块', rank='2'), Card(suit='黑桃', rank='A'), Card(suit='黑桃', rank='7'), Card(suit='方块', rank='Q'), Card(suit='黑桃', rank='9'), Card(suit='红桃', rank='2'), Card(suit='红桃', rank='9'), Card(suit='黑桃', rank='10'), Card(suit='梅花', rank='10'), Card(suit='红桃', rank='3'), Card(suit='红桃', rank='5'), Card(suit='黑桃', rank='K'), Card(suit='梅花', rank='Q')]

对象去重

 class Person:
     def __init__(self, name, age):
         self.name = name
         self.age = age

 p1 = Person('张三', 18)
 p2 = Person('张三', 18)
 print(set([p1, p2]))  # {<__main__.Person object at 0x000000000273DBA8>, <__main__.Person object at 0x000000000273DAC8>}

 class Person:
     def __init__(self, name, age):
         self.name = name
         self.age = age

     def __eq__(self, other):
         return self.name == other.name and self.age == other.age

     def __hash__(self):
         return hash(self.name + str(self.age))

 p1 = Person('张三', 18)
 p2 = Person('张三', 18)
 print(set([p1, p2]))  # {<__main__.Person object at 0x0000000002702860>}

结论:使用set()给对象的去重是同时依赖对象的__hash__()和__eq__()函数的