回到顶部
isinstance和issubclassisinstance(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)
回到顶部
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 *** 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
hasattr
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
getattr
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
setattr
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
delattr
class Foo: f = '类的静态变量'def __init__(self,name,age): self.name=name self.age=agedef 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__)
四个方法的使用演示
class Foo(object): staticFIEld = "old boy" def __init__(self): self.name = 'wupeiqi' def func(self):return 'func' @staticmethoddef bar():return 'bar' print getattr(Foo, 'staticFIEld')print getattr(Foo, 'func')print getattr(Foo, 'bar')
类也是对象
#!/usr/bin/env python# -*- Coding:utf-8 -*-import sysdef s1():print 's1'def s2():print 's2'this_module = sys.modules[__name__]hasattr(this_module, 's1')getattr(this_module, 's2')
反射当前模块成员
导入其他模块,利用反射查找该模块是否存在某个方法
#!/usr/bin/env python# -*- Coding:utf-8 -*-def test():print('from the test')
VIEw Code
#!/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')()
VIEw Code
回到顶部
__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=typedef __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_specif 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'))
VIEw Code
class B: def __str__(self): return 'str : class B' def __repr__(self): return 'repr : class B'b=B()print('%s'%b)print('%r'%b)
%s和%r
回到顶部
__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------->
简单示范
回到顶部
item系列__getitem__\__setitem__\__delitem__class Foo:def __init__(self,name): self.name=namedef __getitem__(self, item):print(self.__dict__[item])def __setitem__(self, key, value): self.__dict__[key]=valuedef __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']=18f1['age1']=19del f1.age1del f1['age']f1['name']='alex'print(f1.__dict__)
VIEw Code
回到顶部
__new__class A:def __init__(self): self.x = 1print('in init function')def __new__(cls, *args, **kwargs):print('in new function')return object.__new__(A, *args, **kwargs)a = A()print(a.x)
VIEw Code
class Singleton:def __new__(cls, *args, **kw):if not hasattr(cls, '_instance'): cls._instance = object.__new__(cls, *args, **kw)return cls._instanceone = 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)单例模式
单例模式
回到顶部
__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):passdef __call__(self, *args, **kwargs):print('__call__')obj = Foo() # 执行 __init__obj() # 执行 __call__
VIEw Code
回到顶部
__len__class A:def __init__(self): self.a = 1self.b = 2def __len__(self):return len(self.__dict__)a = A()print(len(a))
VIEw Code
回到顶部
__hash__class A:def __init__(self): self.a = 1self.b = 2def __hash__(self):return hash(str(self.a)+str(self.b))a = A()print(hash(a))
VIEw Code
回到顶部
__eq__class A:def __init__(self): self.a = 1self.b = 2def __eq__(self,obj):if self.a == obj.a and self.b == obj.b:return Truea = A()b = A()print(a == b)
VIEw Code
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.ranksfor 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
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.ranksfor 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] = valuedeck = FranchDeck()print(deck[0])from random import choiceprint(choice(deck))print(choice(deck))from random import shuffleshuffle(deck)print(deck[:5])
纸牌游戏2
class Person:def __init__(self,name,age,sex): self.name = name self.age = age self.sex = sexdef __hash__(self):return hash(self.name+self.sex)def __eq__(self, other):if self.name == other.name and self.sex == other.sex:return Truep_lst = []for i in range(84): p_lst.append(Person('egon',i,'male'))print(p_lst)print(set(p_lst))
一道面试题
阅读目录isinstance和issubclass反射 setattr delattr getattr hasattr__str__和__repr____del__@L_419_8@ __getitem__ __setitem__ __delitem____new____call____len____hash____eq__
回到顶部
isinstance和issubclassisinstance(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)
回到顶部
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 *** 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
hasattr
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
getattr
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
setattr
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
delattr
class Foo: f = '类的静态变量'def __init__(self,name,age): self.name=name self.age=agedef 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__)
四个方法的使用演示
class Foo(object): staticFIEld = "old boy" def __init__(self): self.name = 'wupeiqi' def func(self):return 'func' @staticmethoddef bar():return 'bar' print getattr(Foo, 'staticFIEld')print getattr(Foo, 'func')print getattr(Foo, 'bar')
类也是对象
#!/usr/bin/env python# -*- Coding:utf-8 -*-import sysdef s1():print 's1'def s2():print 's2'this_module = sys.modules[__name__]hasattr(this_module, 's1')getattr(this_module, 's2')
反射当前模块成员
导入其他模块,利用反射查找该模块是否存在某个方法
#!/usr/bin/env python# -*- Coding:utf-8 -*-def test():print('from the test')
VIEw Code
#!/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')()
VIEw Code
回到顶部
__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=typedef __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_specif 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'))
VIEw Code
class B: def __str__(self): return 'str : class B' def __repr__(self): return 'repr : class B'b=B()print('%s'%b)print('%r'%b)
%s和%r
回到顶部
__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------->
简单示范
回到顶部
item系列__getitem__\__setitem__\__delitem__class Foo:def __init__(self,name): self.name=namedef __getitem__(self, item):print(self.__dict__[item])def __setitem__(self, key, value): self.__dict__[key]=valuedef __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']=18f1['age1']=19del f1.age1del f1['age']f1['name']='alex'print(f1.__dict__)
VIEw Code
回到顶部
__new__class A:def __init__(self): self.x = 1print('in init function')def __new__(cls, *args, **kwargs):print('in new function')return object.__new__(A, *args, **kwargs)a = A()print(a.x)
VIEw Code
class Singleton:def __new__(cls, *args, **kw):if not hasattr(cls, '_instance'): cls._instance = object.__new__(cls, *args, **kw)return cls._instanceone = 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)单例模式
单例模式
回到顶部
__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):passdef __call__(self, *args, **kwargs):print('__call__')obj = Foo() # 执行 __init__obj() # 执行 __call__
VIEw Code
回到顶部
__len__class A:def __init__(self): self.a = 1self.b = 2def __len__(self):return len(self.__dict__)a = A()print(len(a))
VIEw Code
回到顶部
__hash__class A:def __init__(self): self.a = 1self.b = 2def __hash__(self):return hash(str(self.a)+str(self.b))a = A()print(hash(a))
VIEw Code
回到顶部
__eq__class A:def __init__(self): self.a = 1self.b = 2def __eq__(self,obj):if self.a == obj.a and self.b == obj.b:return Truea = A()b = A()print(a == b)
VIEw Code
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.ranksfor 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
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.ranksfor 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] = valuedeck = FranchDeck()print(deck[0])from random import choiceprint(choice(deck))print(choice(deck))from random import shuffleshuffle(deck)print(deck[:5])
纸牌游戏2
class Person:def __init__(self,name,age,sex): self.name = name self.age = age self.sex = sexdef __hash__(self):return hash(self.name+self.sex)def __eq__(self, other):if self.name == other.name and self.sex == other.sex:return Truep_lst = []for i in range(84): p_lst.append(Person('egon',i,'male'))print(p_lst)print(set(p_lst))
一道面试题
总结
以上是内存溢出为你收集整理的python 面向对象-反射全部内容,希望文章能够帮你解决python 面向对象-反射所遇到的程序开发问题。
如果觉得内存溢出网站内容还不错,欢迎将内存溢出网站推荐给程序员好友。
欢迎分享,转载请注明来源:内存溢出
评论列表(0条)