backports.cached-property 1.0.0.post2

cached_property() - computed once per instance, cached as attribute

What

Python 3.8 adds great descriptor to functools: cached_property. Technically all required APIs was available since python 3.6, but it is what it is.

This package is a backport of this functionality for python 3.6 and 3.7.

How to use

from backports.cached_property import cached_property

And then python 3.8 documentation will work (because code is minimally changed):

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.

Example:

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)

Note

This decorator requires that the __dict__ attribute on each instance be a mutable mapping. This means it will not work with some types, such as metaclasses (since the __dict__ attributes on type instances are read-only proxies for the class namespace), and those that specify __slots__ without including __dict__ as one of the defined slots (as such classes don’t provide a __dict__ attribute at all).