Move __len__ and __getitem__ from Parent to FiniteEnumeratedSets

[nthiery]

Title says it all. The point is that with the current implementation prevents categories to override those methods with something more interesting. Alas, the attached patch is not yet ready for consumption since there still remains finite (enumerated) sets in Sage that are not in FiniteSets of FiniteEnumeratedSets (see #12913 and #12957)

In the mean time, #12956 provides a workaround for __getitem__.

Depends on #12957

CC: @sagetrac-sage-combinat @nathanncohen

Component: categories

Branch/Commit: public/12955 @ b6aeeb3

Issue created by migration from https://trac.sagemath.org/ticket/12955

[nthiery]

Preliminary patch

[nthiery]

Description changed:

--- 
+++ 
@@ -1 +1,8 @@
-Title says it all. The point is that with the current implementation in Parent, it is impossible to override those methods with something more interesting from lower categories. This long awaited change should be possible now that all(?) finite enumerated sets in Sage should be in FiniteEnumeratedSets.
+Title says it all. The point is that with the current implementation
+prevents categories to override those methods with something more
+interesting. Alas, the attached patch is not yet ready for
+consumption since there still remains finite (enumerated) sets in Sage
+that are not in FiniteSets of FiniteEnumeratedSets (#)
+
+In the mean time, #12956 provides a workaround for __getitem__.
+

[nthiery]

Dependencies: #12957

[nthiery]

comment:1

Attachment: trac_12955-move_getitem_len_out_of_parent-nt.patch.gz