17、python面向对象进阶
面向对象进阶 isinstance和issubclass isinstance(obj,cls)检查是否obj是否是类 cls 的对象 class Foo(object): pass obj = Foo() isinstance(obj, Foo) issubclass(sub, super)检查sub类是否是 super 类的派生类 class Foo(object): pass class Bar(Foo): pass issubclass(Bar, Foo) 反射 1 什么是反射 反射的概念是由Smith在1982年首次提出的，主要是指程序可以访问、检测和修改它本身状态或行为的一种能力（自省）。这一概念的提出很快引发了计算机科学领域关于应用反射性的研究。它首先被程序语言的设计领域所采用,并在Lisp和面向对象方面取得了成绩。 2 python面向对象中的反射：通过字符串的形式操作对象相关的属性。python中的一切事物都是对象（都可以使用反射） 四个可以实现自省的函数 下列方法适用于类和对象（一切皆对象，类本身也是一个对象） def hasattr(*args, **kwargs): # real signature unknown """ Return whether the object has an attribute with the given name. This is done by calling getattr(obj, name) and catching AttributeError. """ pass 以下实例展示了 hasattr 的使用方法： #!/usr/bin/python# -*- coding: UTF-8 -*- class Coordinate: x = 10 y = -5 z = 0 point1 = Coordinate() print(hasattr(point1, 'x'))print(hasattr(point1, 'y'))print(hasattr(point1, 'z'))print(hasattr(point1, 'no')) # 没有该属性 def getattr(object, name, default=None): # known special case of getattr """ getattr(object, name[, default]) -> value Get a named attribute from an object; getattr(x, 'y') is equivalent to x.y. When a default argument is given, it is returned when the attribute doesn't exist; without it, an exception is raised in that case. """ pass 以下实例展示了 getattr 的使用方法： >>>class A(object): ... bar = 1... >>> a = A()>>> getattr(a, 'bar') # 获取属性 bar 值1>>> getattr(a, 'bar2') # 属性 bar2 不存在，触发异常Traceback (most recent call last): File "<stdin>", line 1, in <module>AttributeError: 'A' object has no attribute 'bar2'>>> getattr(a, 'bar2', 3) # 属性 bar2 不存在，但设置了默认值3 def setattr(x, y, v): # real signature unknown; restored from __doc__ """ Sets the named attribute on the given object to the specified value. setattr(x, 'y', v) is equivalent to ``x.y = v'' """ pass 以下实例展示了 setattr() 函数的使用方法： 实例一 >>>class A(object): ... bar = 1... >>> a = A()>>> getattr(a, 'bar') # 获取属性 bar 值1>>> setattr(a, 'bar', 5) # 设置属性 bar 值>>> a.bar5 实例二 def delattr(x, y): # real signature unknown; restored from __doc__ """ Deletes the named attribute from the given object. delattr(x, 'y') is equivalent to ``del x.y'' """ pass 以下实例展示了 delattr 的使用方法：实例一class Coordinate: x = 10 y = -5 z = 0 point1 = Coordinate() print('x = ',point1.x)print('y = ',point1.y)print('z = ',point1.z) delattr(Coordinate, 'z') print('--删除 z 属性后--')print('x = ',point1.x)print('y = ',point1.y) # 触发错误print('z = ',point1.z) 实例二 class Foo: f = '类的静态变量' def __init__(self,name,age): self.name=name self.age=age def say_hi(self): print('hi,%s'%self.name) obj=Foo('egon',73)#检测是否含有某属性print(hasattr(obj,'name'))print(hasattr(obj,'say_hi'))#获取属性n=getattr(obj,'name')print(n) func=getattr(obj,'say_hi') func()print(getattr(obj,'aaaaaaaa','不存在啊')) #报错#设置属性setattr(obj,'sb',True) setattr(obj,'show_name',lambda self:self.name+'sb')print(obj.__dict__)print(obj.show_name(obj))#删除属性delattr(obj,'age') delattr(obj,'show_name') delattr(obj,'show_name111')#不存在,则报错print(obj.__dict__) 实例三 class Foo(object): staticField = "old boy" def __init__(self): self.name = 'wupeiqi' def func(self): return 'func' @staticmethod def bar(): return 'bar' print getattr(Foo, 'staticField') #获取到属性值print getattr(Foo, 'func') #获取到func的地址print getattr(Foo, 'bar') 实例四 import sys def s1(): print 's1'def s2(): print 's2'this_module = sys.modules[__name__] hasattr(this_module, 's1') getattr(this_module, 's2') 导入其他模块，利用反射查找该模块是否存在某个方法 def test(): print('from the test') """ 程序目录： module_test.py index.py 当前文件： index.py """import module_test as obj#obj.test()print(hasattr(obj,'test')) getattr(obj,'test')() __str__和__repr__ 改变对象的字符串显示__str__,__repr__ 自定制格式化字符串__format__ #_*_coding:utf-8_*_format_dict={ 'nat':'{obj.name}-{obj.addr}-{obj.type}',#学校名-学校地址-学校类型 'tna':'{obj.type}:{obj.name}:{obj.addr}',#学校类型:学校名:学校地址 'tan':'{obj.type}/{obj.addr}/{obj.name}',#学校类型/学校地址/学校名}class School: def __init__(self,name,addr,type): self.name=name self.addr=addr self.type=type def __repr__(self): return 'School(%s,%s)' %(self.name,self.addr) def __str__(self): return '(%s,%s)' %(self.name,self.addr) def __format__(self, format_spec): # if format_spec if not format_spec or format_spec not in format_dict: format_spec='nat' fmt=format_dict[format_spec] return fmt.format(obj=self) s1=School('oldboy1','北京','私立')print('from repr: ',repr(s1))print('from str: ',str(s1))print(s1)''' str函数或者print函数--->obj.__str__() repr或者交互式解释器--->obj.__repr__() 如果__str__没有被定义,那么就会使用__repr__来代替输出 注意:这俩方法的返回值必须是字符串,否则抛出异常 '''print(format(s1,'nat'))print(format(s1,'tna'))print(format(s1,'tan'))print(format(s1,'asfdasdffd')) class B: def __str__(self): return 'str : class B' def __repr__(self): return 'repr : class B'b=B()print('%s'%b)print('%r'%b) __del__ 析构方法，当对象在内存中被释放时，自动触发执行。 注：此方法一般无须定义，因为Python是一门高级语言，程序员在使用时无需关心内存的分配和释放，因为此工作都是交给Python解释器来执行，所以，析构函数的调用是由解释器在进行垃圾回收时自动触发执行的。 class Foo: def __del__(self): print('执行我啦') f1=Foo()del f1print('------->')#输出结果执行我啦 -------> item系列 __getitem__\__setitem__\__delitem__ class Foo: def __init__(self,name): self.name=name def __getitem__(self, item): print(self.__dict__[item]) def __setitem__(self, key, value): self.__dict__[key]=value print("f1['age']=18时,我执行") def __delitem__(self, key): print('del obj[key]时,我执行') self.__dict__.pop(key) def __delattr__(self, item): print('del obj.key时,我执行') self.__dict__.pop(item) f1=Foo('sb') # __dict__[item] 内部是以字典的形式保存数据 # __setitem__设置 key, value f1['age']=18 f1['age1']=19 # __getitem__ 输出设置的值 print(f1.age) # __delattr__ 根据Key删除设置的属性 del f1.age1 # __delitem__ 根据value删除设置的属性 del f1['age'] f1['name']='alex' print(f1.__dict__) __new__ View Code 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) a = A() print(a.x) 单例模式 class Singleton: def __new__(cls, *args, **kw): if not hasattr(cls, '_instance'): cls._instance = object.__new__(cls, *args, **kw) return cls._instance one = Singleton() two = Singleton() two.a = 3print(one.a)# 3 # one和two完全相同,可以用id(), ==, is检测print(id(one))# 29097904print(id(two))# 29097904print(one == two)# Trueprint(one is two) __call__ 对象后面加括号，触发执行。 注：构造方法的执行是由创建对象触发的，即：对象 = 类名() ；而对于 __call__ 方法的执行是由对象后加括号触发的，即：对象() 或者 类()() class Foo: def __init__(self): pass def __call__(self, *args, **kwargs): print('__call__') obj = Foo() # 执行 __init__obj() # 执行 __call__ __len__ class A: def __init__(self): self.a = 1 self.b = 2 def __len__(self): return len(self.__dict__) a = A()print(len(a)) __hash__ class A: def __init__(self): self.a = 1 self.b = 2 def __hash__(self): return hash(str(self.a)+str(self.b)) a = A()print(hash(a)) __eq__ class A: def __init__(self): self.a = 1 self.b = 2 def __eq__(self,obj): if self.a == obj.a and self.b == obj.b: return True a = A() b = A()print(a == b) 纸牌游戏 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','方板','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] deck = FranchDeck()print(deck[0])from random import choiceprint(choice(deck))print(choice(deck)) 纸牌游戏2 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','方板','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 deck = FranchDeck() print(deck[0]) from random import choice print(choice(deck)) print(choice(deck)) from random import shuffle shuffle(deck) print(deck[:5]) 一道面试题 class Person: def __init__(self,name,age,sex): self.name = name self.age = age self.sex = sex def __hash__(self): return hash(self.name+self.sex) def __eq__(self, other): if self.name == other.name and self.sex == other.sex:return True p_lst = []for i in range(84): p_lst.append(Person('egon',i,'male'))print(p_lst)print(set(p_lst))
