do not include parent in hash of parking functions

[mantepse]

We do not want the following:

sage: P = ParkingFunctions(3)
sage: f = P([1,1,1])
sage: g = ParkingFunction([1,1,1])
sage: f in P
True
sage: g in P
True
sage: f in list(P)
True
sage: g in list(P)
True
sage: f in set(P)
True
sage: g in set(P)
False

CC: @nthiery

Component: combinatorics

Author: Martin Rubey

Branch/Commit: 49ff03d

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/34824

[mantepse]

Branch: u/mantepse/do_not_include_parent_in_hash_of_parking_functions

[mantepse]

Commit: ec0577e

[mantepse]

New commits:

ec0577e

do not inherit hash from list_clone.pyx

[mantepse]

Author: Martin Rubey

[nbruin]

comment:3

I expect that you'll have to redefine equality comparison as well: __hash__ and __eq__ go hand-in-hand. See

https://docs.python.org/3/reference/datamodel.html#object.__hash__

You could try to override _hash_ instead, which is the internal routine that is used by the default __hash__ to populate the _hash_ cache attribute.

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

6e8ed10

override `_hash_` instead of __hash__

[sagetrac-git]

Changed commit from ec0577e to 6e8ed10

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

e8abff3	do not include the parent in the hash of CloneableArray and ClonableIntArray, and remove useless overrides
32a2bb4	undo override

[sagetrac-git]

Changed commit from 6e8ed10 to 32a2bb4

[mantepse]

comment:7

I do not understand this - shouldn't the hash be inherited from ClonableArray?

Is this because of metaclass=InheritComparisonClasscallMetaclass?

sage: A = SetPartition([[1],[2,3],[4]])
sage: hash(A)
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In [3], line 1
----> 1 hash(A)

TypeError: unhashable type: 'SetPartitions_all_with_category.element_class'

[mantepse]

comment:8

No, for ParkingFunction, hashing works, even though

class ParkingFunction(ClonableArray, metaclass=InheritComparisonClasscallMetaclass):

[sagetrac-git]

Changed commit from 32a2bb4 to 49ff03d

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. New commits:

49ff03d

check that hash and equality works in DecoratedPermutation, restore hash in OrderedMultisetPartitionIntoSets and AbstractSetPartition

[mantepse]

comment:10

See also https://groups.google.com/g/sage-devel/c/0J2jiBh5AvE

[tscrim]

comment:11

LGTM. This will make handling equality easier for subclasses.

Note that this will cause a slight performance regression when there is hashing involving things that are represented by the same list but should not be compared. For example [3, 2, 1] as a permutation versus as a partition (if they both inherited from ClonableArray). However, I don't see this having a practical effect and it is still outweighed by the ease-of-use IMO.

[tscrim]

Reviewer: Travis Scrimshaw

[vbraun]

Changed branch from u/mantepse/do_not_include_parent_in_hash_of_parking_functions to 49ff03d