python的getattr和getattribute拦截内置操作实现

>>> class SquareCubePro:
    '''
        property 特性计算平方和立方
        前下化线开头属性名存储基础数据
        赋值为特性的属性名不带下划线
        self._square和square=property：
        实例属性和特性属性不能同名，避免循环
    '''
    def __init__(self,sq,cu):
        self._square=sq
        self._cube=cu
    def getSquare(self):
        return self._square**2
    def setSquare(self,value):
        self._square=value
    square=property(getSquare,setSquare)
    
    def getCube(self):
        return self._cube**3
    cube=property(getCube)

    
>>> scp=SquareCubePro(2,3)
>>> scp.square,scp.cube
(4, 27)
>>> scp=SquareCubePro(3,5)
>>> scp.square,scp.cube
(9, 125)
>>> scp.square=5
>>> scp.square
25



>>> class SquareDesc:
    '''
        Descriptor 描述符计算平方和立方
        基础数据存储在客户类实例的属性上
    '''
    def __get__(self,instance,owner):
        return instance._square**2
    def __set__(self,instance,value):
        instance._square=value

        
>>> class CubeDesc:
    def __get__(self,instance,owner):
        return instance._cube**3

    
>>> class SquareCubeDesc:
    sq=SquareDesc()
    cu=CubeDesc()
    def __init__(self,sq,cu):
        self._square=sq
        self._cube=cu

        
>>> scd=SquareCubeDesc(3,5)
>>> scd.sq,scd.cu
(9, 125)
>>> scd.sq=5
>>> scd.sq
25

>>> class SquareCubeGetA:
    '''
        重载 __getattr__ 计算平方和立方
    '''
    def __init__(self,sq,cu):
        self._square=sq
        self._cube=cu
    def __getattr__(self,name):
        if name=='square':
            return self._square**2
        elif name=='cube':
            return self._cube**3
        else:
            raise TypeError('属性错误:',name)
    def __setattr__(self,name,value):
        if name=='square':
            self.__dict__['_square']=value
        else:
            self.__dict__[name]=value

            
>>> scga=SquareCubeGetA(3,5)
>>> scga.square,scga.cube
(9, 125)
>>> scga.square=5
>>> scga.square
25

>>> class SquareCubeGetAB:
    '''
        重载 __getattribute__ 计算平方和立方
    '''
    def __init__(self,sq,cu):
        self._square=sq
        self._cube=cu
    def __getattribute__(self,name):
        if name=='square':
            return object.__getattribute__(self,'_square')**2
        elif name=='cube':
            return object.__getattribute__(self,'_cube')**3
        else:
            return object.__getattribute__(self,name)
    def __setattr__(self,name,value):
        if name=='square':
            self.__dict__['_square']=value
        else:
            self.__dict__[name]=value

            
>>> scgab=SquareCubeGetAB(3,5)
>>> scgab.square,scgab.cube
(9, 125)
>>> scgab.square=5
>>> scgab.square
25

S.center(width[, fillchar]) -> string

>>> strL=['MyGetAttr','MyGetAttribute']
>>> for s in strL:
    print('\n'+s.center(50,'='))
    print('test center')

====================MyGetAttr=====================
test center

==================MyGetAttribute==================
test center

# encoding:utf-8

class MyGetAttr:
    name='梯阅线条'
    def __init__(self):
        self.url='tyxt.work'
    def __len__(self):
        print('__len__:9555')
        return 9555
    def __getattr__(self,attr):
        print('__getattr__:'+attr)
        if attr == '__str__':
            return lambda *args:'[GetAttr str]'
        else:
            return lambda *args:None

        
class MyGetAttribute(object):
    name='梯阅线条'
    def __init__(self):
        self.url='tyxt.work'
    def __len__(self):
        print('__len__:9555')
        return 9555
    def __getattribute__(self,attr):
        print('__getattribute__:'+attr)
        if attr == '__str__':
            return lambda *args:'[Getattribute str]'
        else:
            return lambda *args:None

if __name__=='__main__':     
    import sys
    print('python '+sys.version.split()[0])
    for C in MyGetAttr,MyGetAttribute:
        print('\n'+C.__name__.center(50,'='))
        c1=C()
        c1.name
        c1.url
        c1.tel
        len(c1)
        try:
            c1[0]
        except:
            print('fail []')
        try:
            c1+99
        except:
            print('fail +')
        try:
            c1()
        except:
            print('fail ()')
        c1.__call__()
        print(c1.__str__())
        print(c1)

C:\Users\Administrator>D:\Python27\python.exe E:\documents\F盘\testgetattr.py
python 2.7.18

====================MyGetAttr=====================
__getattr__:tel
__len__:9555
__getattr__:__getitem__
__getattr__:__coerce__
__getattr__:__add__
__getattr__:__call__
__getattr__:__call__
__getattr__:__str__
[GetAttr str]
__getattr__:__str__
[GetAttr str]

==================MyGetAttribute==================
__getattribute__:name
__getattribute__:url
__getattribute__:tel
__len__:9555
fail []
fail +
fail ()
__getattribute__:__call__
__getattribute__:__str__
[Getattribute str]
<__main__.MyGetAttribute object at 0x00000000034B7C88>

C:\Users\Administrator>D:\Python3\python.exe E:\documents\F盘\testgetattr.py
python 3.7.8

====================MyGetAttr=====================
__getattr__:tel
__len__:9555
fail []
fail +
fail ()
__getattr__:__call__
<__main__.MyGetAttr object at 0x01648E10>
<__main__.MyGetAttr object at 0x01648E10>

==================MyGetAttribute==================
__getattribute__:name
__getattribute__:url
__getattribute__:tel
__len__:9555
fail []
fail +
fail ()
__getattribute__:__call__
__getattribute__:__str__
[Getattribute str]
<__main__.MyGetAttribute object at 0x01648F50>