memoized_property.py

class memoized_property:
    def __init__(self, method):
        self.__method = method
        prefix = method.__qualname__.rsplit(".")[0].replace(".", "__")
        self.__name = '_%s__%s' % (prefix, method.__name__)

    def __get__(self, obj, objtype=None):
        if obj is None:
            return self

        try:
            value = getattr(obj, self.__name)
        except AttributeError:
            value = self.__method(obj)
            setattr(obj, self.__name, value)

        return value