飘逸的python - __get__ vs __getattr__ vs __getattribute__以及属性的搜索策略

差别:

__getattribute__:是无条件被调用.对不论什么对象的属性訪问时,都会隐式的调用__getattribute__方法,比方调用t.__dict__,事实上运行了t.__getattribute__("__dict__")函数.所以假设我们在重载__getattribute__中又调用__dict__的话,会无限递归,用object大神来避免,即object.__getattribute__(self, name).

属性的lookup顺序例如以下:

1. 假设重载了__getattribute__,则调用.
2. a.__dict__, 实例中是不同意有descriptor的,所以不会遇到descriptor
3. A.__dict__, 也即a.__class__.__dict__ .假设遇到了descriptor,优先调用descriptor.
4. 沿着继承链搜索父类.搜索a.__class__.__bases__中的全部__dict__. 假设有多重继承且是菱形继承的情况,按MRO(Method Resolution Order)顺序搜索.

以下给个代码片段大家自己去把玩探索.

class C(object):
    def __setattr__(self, name, value):
        print "__setattr__ called:", name, value
        object.__setattr__(self, name, value)

    def __getattr__(self, name):
        print "__getattr__ called:", name

    def __getattribute__(self, name):
        print "__getattribute__ called:",name
        return object.__getattribute__(self, name)

c = C()
c.x = "foo"
print c.__dict__['x']
print c.x