属性搜索优先级和 descriptor

########################
# 定义
########################
 
# 数据描述符
class DataDesc(object):
    def __init__(self, *args, **kwargs):
        pass
 
    def __get__(self, instance, cls):
        print(instance is None)
        return 'DataDesc'
 
    def __set__(self, instance, value):
        return None
 
    def __delete__(self, instance):
        return None
 
 
# 数据描述符
class DataDesc2(object):
    def __init__(self, *args, **kwargs):
        pass
 
    def __get__(self, instance, cls):
        return 'DataDesc2'
 
    def __set__(self, instance, value):
        return None
 
 
# 非数据描述符
class NonDataDesc(object):
    def __init__(self, *args, **kwargs):
        pass
 
    def __get__(self, instance, cls):
        print(instance is None)
        return 'NonDataDesc'
 
 
class Foo(object):
    test_attr = DataDesc()
    test_attr2 = DataDesc()
    test_attr3 = NonDataDesc()
    test_attr4 = 'test_attr4'
 
    def __getattr__(self, item):
        return 'hehe__getattr__'
 
 
########################
# 一般情况
########################
foo = Foo()
'''1. foo.__dict__['test_attr4']
2. for cls in Foo.__mro__:
       cls.__dict__['test_attr4']
3. foo.__getattr__('test_attr4')
'''
print(foo.test_attr4)
foo.__dict__['test_attr4'] = 666
print(foo.test_attr4)
print(id(foo.test_attr4) == id(foo.__dict__['test_attr4']))
foo.__dict__.pop('test_attr4')
print(foo.test_attr4)
print(foo.test_attr5)
print(foo.__getattr__('test_attr5'))
 
########################
# 数据型描述符
########################
foo = Foo()
'''1. type(foo).__dict__['test_attr'].__get__(foo, type(foo))
2. foo.__dict__['test_attr4']
3. for cls in Foo.__mro__:
       cls.__dict__['test_attr4']
4. foo.__getattr__('test_attr4')
'''
print(foo.test_attr)
foo.__dict__['test_attr'] = 666
print(foo.test_attr)
print(id(foo.test_attr) == id(foo.__dict__['test_attr']))
delattr(Foo, 'test_attr')
print(foo.test_attr)
print(id(foo.test_attr) == id(foo.__dict__['test_attr']))
 
########################
# 非数据型描述符
########################
foo = Foo()
'''1. foo.__dict__['test_attr4']
2. type(foo).__dict__['test_attr'].__get__(foo, type(foo))
3. for cls in Foo.__mro__:
       cls.__dict__['test_attr4']
4. foo.__getattr__('test_attr4')
'''
print(foo.test_attr3)
foo.__dict__['test_attr3'] = 666
print(foo.test_attr3)
print(id(foo.test_attr3) == id(foo.__dict__['test_attr3']))
del foo.test_attr3
print(foo.test_attr3)
 
########################
# 类调用描述符
########################
'''FOO.__dict__['test_attr'].__get__(None, FOO)'''
print(Foo.test_attr2)
print(Foo.test_attr3)
 
########################
# __getattribute__
########################
'''
如果被重写, 上面代码介绍的东西会被覆盖掉
除非函数内部调用 object.__getattribute__
否则别这么干
'''
 
 
class Foo2(object):
    test_attr = DataDesc()
    test_attr2 = DataDesc()
    test_attr3 = NonDataDesc()
    test_attr4 = 'test_attr4'
 
    def __getattribute__(self, item):
        return 'in __getattribute__'
 
 
foo = Foo2()
print(foo.test_attr3)
 
########################
# 例子
########################
import time
 
 
class LazyProperty(object):
    def __init__(self, func):
        self.func = func
 
    def __get__(self, instance, cls):
        if instance is not None:
            val = self.func(instance)
            setattr(instance, self.func.__name__, val)
            return val
 
 
class Foo3(object):
    @LazyProperty
    def method(self):
        time.sleep(5)
        return 666
 
 
foo3 = Foo3()
time1 = time.time()
print(foo3.method)
time2 = time.time()
print(time2 - time1)
print(foo3.method)
print(time.time() - time2)