cached_property的理解和使用

class A(object):    def __init__(self):        pass    def random(self):        return random.random()class B(object):    @cached_property    def a(self):        return A()

>>> b = B()>>> b.a.random()>>> b.a.other_method()

>>> b = B()>>> a = b.a()>>> a.random()>>> a.other_method()

class B(object):    @cached_property    def a(self):        return A()    @cached_property    def c(self):        return C()

class _Missing(object):    def __repr__(self):        return 'no value'    def __reduce__(self):        return '_missing'_missing = _Missing()class cached_property(property):    def __init__(self, func, name=None, doc=None):        self.__name__ = name or func.__name__        self.__module__ = func.__module__        self.__doc__ = doc or func.__doc__        self.func = func    def __set__(self, obj, value):        obj.__dict__[self.__name__] = value    def __get__(self, obj, type=None):        if obj is None:            return self        value = obj.__dict__.get(self.__name__, _missing)        if value is _missing:            value = self.func(obj)            obj.__dict__[self.__name__] = value        return value

class cached_property:    """ thread safe cached property """    def __init__(self, func, name=None):        self.func = func        self.__doc__ = getattr(func, '__doc__')        self.name = name or func.__name__        self.lock = Lock()    def __get__(self, instance, cls=None):        with self.lock:            if instance is None:                return self            try:                return instance.__dict__[self.name]            except KeyError:                res = instance.__dict__[self.name] = self.func(instance)                return res

class B(object):    @cached_property    def b(self):        pass

class cached_property:    """ thread safe cached property """    def __init__(self, func, name=None):        self.func = func # 这个func对应上面的就为b        self.__doc__ = getattr(func, '__doc__') # None        self.name = name or func.__name__ # func.__name__ 为b

class Property(object):    "Emulate PyProperty_Type() in Objects/descrobject.c"    def __init__(self, fget=None, fset=None, fdel=None, doc=None):        self.fget = fget        self.fset = fset        self.fdel = fdel        if doc is None and fget is not None:            doc = fget.__doc__        self.__doc__ = doc    def __get__(self, obj, objtype=None):        if obj is None:            return self        if self.fget is None:            raise AttributeError("unreadable attribute")        return self.fget(obj)    def __set__(self, obj, value):        if self.fset is None:            raise AttributeError("can't set attribute")        self.fset(obj, value)    def __delete__(self, obj):        if self.fdel is None:            raise AttributeError("can't delete attribute")        self.fdel(obj)    def getter(self, fget):        return type(self)(fget, self.fset, self.fdel, self.__doc__)    def setter(self, fset):        return type(self)(self.fget, fset, self.fdel, self.__doc__)    def deleter(self, fdel):        return type(self)(self.fget, self.fset, fdel, self.__doc__)

def __get__(self, instance, cls=None):        # instance代表实例化B        with self.lock:            if instance is None:                return self            try:                return instance.__dict__[self.name]            except KeyError:                 # 如果没有在B的__dict__找到self.name(即方法b), 那么self.func(即方法b)则会执行b(B), 并将其保存到实例化b的__dict__下                res = instance.__dict__[self.name] = self.func(instance)                return res

class B(object):    @cached_property    def a(self):        return A()    @cached_property    def c(self):        return C()>>> b = B()>>> for i in range(3):        print(b.__dict__)        b.a.random()

# 类版本的计算时间的装饰器class cal_time(object):    def __init__(self, func):        self.func = func    def __call__(self, *args, **kwargs):        s = time.time()        resp = self.func(*args, **kwargs)        e = time.time()        print("使用时长:{}".format(e - s))        return resp