day_06、面向对象(二)
isinstance和issubclass
isinstance(obj.cls)检查obj是否是类cls的对象
class Foo(object): pass obj = Foo() print(isinstance(obj, Foo))
issubclass(sub, super)检查sub类是否是euper类的派生类
class Foo(object): pass class Bar(Foo): pass print(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:通过字符串形式操作对象相关的属性。在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)
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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
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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
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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
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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
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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,{}. ".format(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, 'aaaa', '不存在的')) # 设置属性 setattr(obj, 'sb', True) setattr(obj, 'show_name', lambda self:self.name + 'sb') print(obj.__dict__) print(obj.show_name) # 删除属性 delattr(obj, 'age') delattr(obj, 'show_name') delattr(obj, "show_name111") print(obj,__dict__)
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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')) print(getattr(Foo, 'func')) print(getattr(Foo, 'bar'))
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import sys def s1(): print('s1') def s2(): print('s2') this_moudle = sys.modules[__name__] print(hasattr(this_moudle, 's1')) print(hasattr(this_moudle, 's2'))
导入其他模块,利用反射查找该模块是否存在某个方法
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#-*- coding:utf-8 -*- #version: 3.6.4 def test(): print('from the test')
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#-*- coding:utf-8 -*- #version: 3.6.4 """ 程序目录: module_test.py index.py 当前文件: index.py """ import module_test as obj print(hasattr(obj, 'test')) # True getattr(obj, 'test')() # from the 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__
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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 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'))
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class B: def __str__(self): return 'str: class B' def __repr__(self): return 'repr: class B' b = B() print('%s' %b) print('%r' %b) ''' str: class B repr: class B '''
__del__
析构方法,当对象在内存中被释放时,自动触发执行。
注:此方法一般无需定义,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。
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class Foo: def __del__(self): print("执行我啦") f1 = Foo() del f1 print('--->') ''' 执行我啦 ---> '''
item系列
__getitem__、 __setitem__ 、 __delitem__
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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,执行我") self.__dict__.pop(key) def __delattr__(self, item): self.__dict__.pop(item) f1 = Foo('sb') f1['age'] = 18 f1['age1'] = 19 print(f1.__dict__) del f1.age1 print(f1.__dict__) del f1['age'] f1['name'] = 'alex' print(f1.__dict__) ''' {'name': 'sb', 'age': 18, 'age1': 19} {'name': 'sb', 'age': 18} del obj[key]时,执行我 {'name': 'alex'} '''
__new__
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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) ''' in new function in init function 1 '''
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class Singleton: def __new__(cls, *args, **kwargs): if not hasattr(cls, '_instance'): cls._instance = object.__new__(cls, *args, **kwargs) return cls._instance one = Singleton() two = Singleton() two.a = 3 print(one.a) print(id(one)) print(id(two)) print(one is two) ''' 3 89634128 89634128 True '''
__call__
对象后面加括号。触发执行。
注:构造方法的执行时由创建对象触发的,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()()
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class Foo: def __init__(self): pass def __call__(self, *args, **kwargs): print('__call__') obj = Foo() obj() # 注释__call__方法 报错'Foo' object is not callable ''' __call__ '''
__len__
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class A: def __init__(self): self.a = 1 self.b = 2 def __len__(self): print(self.__dict__) return len(self.__dict__) a = A() print(len(a)) ''' {'a': 1, 'b': 2} 2 '''
__hash__
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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)) # 注释掉__hash__不报错
__eq__
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class A: def __init__(self): self.a = 1 self.b = 2 def __eq__(self, other): if self.a == other.a and self.b == other.b: return True a = A() b = A() print(a == b) # 注释掉__eq__ False
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import collections Card = collections.namedtuple('Card', ['rank', 'suit']) class FranchDeck: ranks = [str(n) for n in range(2, 11)] + list('JQKA') suits = ['红心', '方片', '梅花', '黑桃'] def __init__(self): self._cards = [Card(rank, suit) for rank in self.ranks for suit in self.suits] def __len__(self): return len(self._cards) def __getitem__(self, item): return self._cards[item] deck = FranchDeck() print(deck.__dict__) from random import choice print(choice(deck)) print(choice(deck))
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import collections Card = collections.namedtuple('Card', ['rank', 'suit']) class FranchDeck: ranks = [str(n) for n in range(2, 11)] + list('JQKA') suits = ['红心', '方片', '梅花', '黑桃'] def __init__(self): self._cards = [Card(rank, suit) for rank in self.ranks for suit in self.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.__dict__) from random import choice print(choice(deck)) print(choice(deck)) from random import shuffle shuffle(deck) print(deck[:5])
懵逼
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))