Cached property and cached callable

cachedproperty.py

import sys
import types


class cachedproperty(object):
    __slots__ = ('fget', 'name', '__doc__')

    def __init__(self, fget, doc=None):
        self.fget = fget
        self.name = fget.__name__  # python < 3.6
        if doc is None:
            doc = fget.__doc__
        self.__doc__ = doc

    def __set_name__(self, owner, name):
        self.name = name

    def __get__(self, instance, owner=None):
        if instance is None:
            return self
        value = self.fget(instance)
        setattr(instance, self.name, value)
        return value


class cachedcallable(object):
    __slots__ = ('fget', 'name', '__doc__')

    def __init__(self, fget, doc=None):
        self.fget = fget
        self.name = fget.__name__  # python < 3.6
        if doc is None:
            doc = fget.__doc__
        self.__doc__ = doc

    def __set_name__(self, owner, name):
        self.name = name

    def __get__(self, instance, owner=None):
        if instance is None:
            return self
        value = self.fget(instance)

        def wrap(self):
            return value

        wrap.__doc__ = self.__doc__
        if sys.version_info.major == 2:
            wrap = types.MethodType(wrap, instance, type(instance))
        else:
            wrap = types.MethodType(wrap, instance)

        setattr(instance, self.name, wrap)
        return wrap


class Demo(object):
    @cachedproperty
    def answer(self):
        print('answer called')
        return 42

    @cachedcallable
    def get_answer(self):
        print('get_answer called')
        return 42


if __name__ == '__main__':
    d = Demo()
    print(d.answer)
    print(d.answer)
    print(d.answer)
    print(d.get_answer())
    print(d.get_answer())
    print(d.get_answer())
    print(d.get_answer)

answer called
42
42
42
get_answer called
42
42
42
<bound method cachedcallable.__get__.<locals>.wrap of <__main__.Demo object at 0x7fb89af32908>>