python(第五天):__getattr__ 和 __getattribute__

This chapter I plan to write by English. 如果有什么错误欢迎指正.

I will talk about the difference between __getattr__(self,name)  and __getattribute__(self,name)

Firstly look at the description of __getattr__:

Called when an attribute lookup has not found the attribute in the usual places(i.e. it is not an instance attribute nor is it found in the class tree for self).

arguments:name is the attribute name

This method should return the (computed) attribute value or raise an AttributeErrorexception.

就是说如果在实例的搜索树中没有找到这个属性就调用__getattr__(self,name)

这里要注意一点私有成员的实现方式是_ClassName__attributeName所以当调用__attributeName时也会触发__getattri__.

look at the description of  __getattribute__:

Called unconditionally to implement attribute accesses for instances of the class. If the class also defines __getattr__(),the latter will not be called unless __getattribute__() either calls it explicitly or raises an AttributeError.

无条件被调用，通过实例访问属性。如果class中定义了__getattr__()，则__getattr__()不会被调用（除非显示调用或引发AttributeError异常）

    def __getattribute__(self, *args, **kwargs):         print("__getattribute__() is called") #         return object.__getattribute__(self, *args, **kwargs)         raise AttributeError    def __getattr__(self, name):         print("__getattr__() is called ")         return name + " from getattr"

如果在上面的代码中 没有 raise AttributeError则不会触发__getattr__