python之路——面向对象进阶

阅读量：5326 次

发布时间：2019-06-14

本文共 7834 字，大约阅读时间需要 26 分钟。

阅读目录

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()  sinstance(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

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=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__)

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'     @staticmethod    def 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

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'))

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

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

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    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']=18f1['age1']=19del f1.age1del f1['age']f1['name']='alex'print(f1.__dict__)

View Code

new

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)

View Code

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._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

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()()

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()()

View Code

len

class A:    def __init__(self):        self.a = 1        self.b = 2    def __len__(self):        return len(self.__dict__)a = A()print(len(a))

View Code

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))

View Code

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 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.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

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] = 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 = 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 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

转载于:https://www.cnblogs.com/zhangningyang/p/7373691.html

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