python之路——面向对象进阶

一、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)

二、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。

 

python面向过程、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）

2.1 hasattr

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

2.2 getattr

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

2.3 setattr

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

2.4 delattr

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

2.5 四个方法的使用演示

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__)

2.6 类也是对象

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')

2.7 反射当前模块成员

#!/usr/bin/env python
# -*- coding:utf-8 -*-import sysdef s1():print('s1')def s2():print('s2')# this_module = sys.modules["__main__"]   这种写法只能在这个文件中调用，在其他文件中调用，由于__main__被写死，所以要改成下面的 __name__就是字符串“__main__”
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个方法

#!/usr/bin/env python
# -*- coding:utf-8 -*-def test():print('from the test')------------------------------------------------
#!/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')()

要反射的函数有参数怎么办?

import time
print(time.strftime('%Y-%m-%d %H:%M:S'))
print(getattr(time,'strftime')('%Y-%m-%d %H:%M:S'))

一个模块中的类能不能反射得到

import my
print(getattr(my,'C')())
if hasattr(my,'name'):getattr(my,'name')

2.8 setattr  设置修改变量

class A:pass
a = A()
setattr(a,'name','nezha')
setattr(A,'name','alex')
print(A.name)
print(a.name)

2.9 delattr 删除一个变量

delattr(a,'name')
print(a.name)
delattr(A,'name')
print(a.name)

python 面向对象。