Doc: Add missing entry for functools.cached_property (pythonGH-16803)

Author: matrixise

Doc/whatsnew/3.8.rst

@@ -683,6 +683,22 @@ than as a function returning a decorator. So both of these are now supported::
 
 (Contributed by Raymond Hettinger in :issue:`36772`.)
 
+Added a new :func:`functools.cached_property` decorator, for computed properties
+cached for the life of the instance. ::
+
+ import functools
+ import statistics
+
+ class Dataset:
+ def __init__(self, sequence_of_numbers):
+ self.data = sequence_of_numbers
+
+ @functools.cached_property
+ def variance(self):
+ return statistics.variance(self.data)
+
+(Contributed by Carl Meyer in :issue:`21145`)
+
 
 gc
 --