python-自定義property,支持緩存

my_property

class my_property:
    def __init__(self, fget=None, fset=None, fdel=None, cache=False):
        self.fget = fget
        self.fset = fset
        self.fdel = fdel
        self.cache = cache

    def setter(self, func):
        if self.cache:
            raise ValueError("'setter' require cache is False")

        if self.fget is None:
            raise ValueError("descriptor 'setter' requires a 'property' object but received a 'function'")
        self.fset = func

    def deleter(self, func):
        if self.fget is None and self.fset is None:
            raise ValueError("TypeError: descriptor 'deleter' requires a 'property' object but received a 'function'")
        self.fdel = func

    def __get__(self, instance, owner):
        if instance is None:
            return self
        value = self.fget(instance)
        if self.cache:
            instance.__dict__[self.fget.__name__] = value
        return value

    def __call__(self, func):
        self.fget = func
        return self


class Rectangle:
    def __init__(self, width, height):
        self.width = width
        self.height = height

    @my_property(cache=True)
    def area(self):
        print('============計算面積啦============')
        return self.width*self.height

    @my_property
    def perimeter(self):
        print('------------計算周長啦------------')
        return (self.width + self.height) * 2


a = Rectangle(3, 4)
print(a.area)
print(a.area)

print(a.perimeter)
print(a.perimeter)

結果如下

/usr/bin/python3.6 /home/sunsong/Desktop/Demo/C.py
============計算面積啦============
12
12
------------計算周長啦------------
14
------------計算周長啦------------
14

可以看到設置緩存的沒有進行第二次計算，而沒有設置緩存的進行了兩次計算。