Implements a variant of @cached_method with cache stored in the parent

[nthiery]

When the elements of a parent do not have unique representation, it
can be desirable to store the cache of (some of) the methods in the
parent rather than in the element.

This patches implements a variant @cached_in_parent_method of the
decorator @cached_method which does just this.

CC: @sagetrac-sage-combinat

Component: misc

Keywords: cached_method, cache

Issue created by migration from https://trac.sagemath.org/ticket/5449

[nthiery]

Changed keywords from none to cached_method, cache

[nthiery]

Description changed:

--- 
+++ 
@@ -1,7 +1,7 @@
-When the elements of a parent do not have unique representation, it can be desirable to store the cache of (some of) the methods in the parent rather than in the element.
+When the elements of a parent do not have unique representation, it
+can be desirable to store the cache of (some of) the methods in the
+parent rather than in the element.
 
-Comments, suggestions?
+This patches implements a variant `@`cached_in_parent_method of the
+decorator `@`cached_method which does just this.
 
-`@`cached_in_parent_method ?
-
-I'll write a quick patch in sage-combinat

[nthiery]

comment:2

Attachment: cached_in_parent_method-5449-submitted.patch.gz

[roed314]

comment:3

Passes doctests, good documentation.