python之路——面向对象进阶

阅读目录

isinstance和issubclass
反射
- 　　setattr
- 　　delattr
- 　　getattr
- 　　hasattr
__str__和__repr__
__del__
item系列
- 　　__getitem__
- 　　__setitem__
- 　　__delitem__
__new__
__call__
__len__
__hash__
__eq__

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isinstance和issubclass

isinstance(obj,cls)检查是否obj是否是类 cls 的对象

class Foo(object):passobj = Foo()isinstance(obj, Foo)

issubclass(sub, super)检查sub类是否是 super 类的派生类

class Foo(object):passclass Bar(Foo):passissubclass(Bar, Foo)

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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]) -> valueGet 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'texist; 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=nameself.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.pyindex.py当前文件：index.py
"""import module_test as obj#obj.test()print(hasattr(obj,'test'))getattr(obj,'test')()

View Code

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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=nameself.addr=addrself.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

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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 f1
print('------->')#输出结果
执行我啦
------->

简单示范

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

View Code

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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 = 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)单例模式

单例模式

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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__

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len

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

View Code

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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

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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 True
a = 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 choice
print(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 choice
print(choice(deck))
print(choice(deck))from random import shuffle
shuffle(deck)
print(deck[:5])

纸牌游戏2

class Person:def __init__(self,name,age,sex):self.name = nameself.age = ageself.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))