面向对象进阶
isinstance() issubclass()
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
class Foo: pass class Son(Foo): pass s=Son() isinstance() 判读一个对象是不是这个类的对象 print(isinstance(s,Son)) #s是不是Son的对象 print(isinstance(s,Foo)) print(type(s) is Son) print(type(s) is Foo) issubclass()判断一个类是不是另一个的子类(传两个参数(子类、父类)) print(issubclass(Son,Foo)) print(issubclass(Son,object)) print(issubclass(Foo,object)) print(issubclass(int,object))
反射
指程序可以访问、检测和修改它本身的一种能力
python面向对象中的反射:通过与字符串的形式操作对象的相关属性,Python中一切皆对象(都可以使用反射)
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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__)
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
#!/usr/bin/env python # -*- coding:utf-8 -*- 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方法
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
#!/usr/bin/env python # -*- coding:utf-8 -*- def test(): print('from the test')
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
#!/usr/bin/env python # -*- coding:utf-8 -*- """ 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')()
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
class Foo:
def __init__(self):
self.name='egon'
self.age=73
def func(self):
print(123)
l=Foo()
print(l.name)
l.func()
if hasattr(l,'func'):
Foo__func=getattr(l,'func')
Foo__func()
print(l.__dict__['name']) #用字符串的形式取类里面的属性.不能一字符串的形式拿方法
print(hasattr(l,'name'))
print(getattr(l,'name'))
setattr(l,'sex','属性值')
print(l.sex)
def show_name(self):
print(self.name+'sb') #这里还是没有实现,课下找答案
setattr(l,'show_name',lambda self:self.name+'sb')
l.show_name(l)
print()
常用
hasattr #f返回布尔值
getattr #如果存在这个方法或者属性,就返回属性值或者方法的内存地址
不存在报错,因此和hasattr搭配使用
不常用
setattr
delattr.
delattr(l,'name') #不能删除类里的方法
print(l.name)
可以与字符串的方式去访问对象的属性、调用对象的方法
__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
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
#_*_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'))
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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。
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
class B: def __str__(self): return 'str : class B' def __repr__(self): return 'repr : class B' b=B() print('%s'%b) print('%r'%b)
item系列
__getitem__\__setitem__\__delitem__
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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 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') f1['age']=18 f1['age1']=19 del f1.age1 del f1['age'] f1['name']='alex' print(f1.__dict__)
__new__
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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)
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
class Singleton: def __new__(cls, *args, **kw): if not hasattr(cls, '_instance'): orig = super(Singleton, cls) cls._instance = orig.__new__(cls, *args, **kw) return cls._instance one = Singleton() two = Singleton() two.a = 3 print(one.a) # 3 # one和two完全相同,可以用id(), ==, is检测 print(id(one)) # 29097904 print(id(two)) # 29097904 print(one == two) # True print(one is two)
__call__
对象后面加括号,触发执行。
构造方法的执行是由创建对象触发的
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
class Foo: def __init__(self): pass def __call__(self, *args, **kwargs): print('__call__') obj = Foo() # 执行 __init__ obj() # 执行 __call__
__len__
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
class A: def __init__(self): self.a = 1 self.b = 2 def __len__(self): return len(self.__dict__) a = A() print(len(a))
__hash__
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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__
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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)
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
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))