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):
     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)

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。

 

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]) -> 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

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=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__)

2.6 类也是对象

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'))  # old boy
print(getattr(Foo, 'func'))         # <function Foo.func at 0x00000271A012DE18>
print(getattr(Foo, 'bar'))          # <function Foo.bar at 0x00000271A012E488>
setattr(Foo,"func","sss")   
print(getattr(Foo, 'func'))         # sss

2.7 反射当前模块成员

#!/usr/bin/env python
# -*- coding:utf-8 -*-

import sys


def 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.py
    index.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)