Caching class attributes in Python

Question

I\'m writing a class in python and I have an attribute that will take a relatively long time to compute, so I only want to do it once. Also, it will not be

Answer 1

Python 3.8 includes the functools.cached_property decorator.

Transform a method of a class into a property whose value is computed once and then cached as a normal attribute for the life of the instance. Similar to property(), with the addition of caching. Useful for expensive computed properties of instances that are otherwise effectively immutable.

This example is straight from the docs:

from functools import cached_property

class DataSet:
    def __init__(self, sequence_of_numbers):
        self._data = sequence_of_numbers

    @cached_property
    def stdev(self):
        return statistics.stdev(self._data)

    @cached_property
    def variance(self):
        return statistics.variance(self._data)

The limitation being that the object with the property to be cached must have a __dict__ attribute that is a mutable mapping, ruling out classes with __slots__ unless __dict__ is defined in __slots__.