class lazyproperty:
    def __init__(self, func):
        self.func = func
    def __get__(self, instance, cls):
        if instance is None:
            return self
        else:
            value = self.func(instance)
            setattr(instance, self.func.__name__, value)
            return value
        
if __name__ == '__main__':
    import math
    class Circle:
        def __init__(self, radius):
            self.radius = radius

        @lazyproperty
        def area(self):
            print('Computing area')
            return math.pi * self.radius ** 2

        @lazyproperty
        def perimeter(self):
            print('Computing perimeter')
            return 2 * math.pi * self.radius