py3: hashing of cartesian product elements

[dkrenn]

part of #24551

sage: C = cartesian_product([ZZ,ZZ])
sage: b = C((1,1))
sage: hash(b)
---------------------------
TypeError      Traceback (most recent call last)
<ipython-input-1-b09cf2f9caf6> in <module>()
      1 C = cartesian_product([ZZ,ZZ])
      2 b = C((Integer(1),Integer(1)))
----> 3 hash(b)

TypeError: unhashable type: 'CartesianProduct_with_category.element_class'

Component: python3

Author: Frédéric Chapoton

Branch/Commit: bc571fd

Reviewer: Travis Scrimshaw

Issue created by migration from https://trac.sagemath.org/ticket/26145

[fchapoton]

comment:2

indeed, hash does not exist, even if it appears in the tab completion:

sage: A = cartesian_product([ZZ, ZZ])
sage: elt = A((1,1))
sage: elt.__eq__
<method-wrapper '__eq__' of CartesianProduct_with_category.element_class object at 0x7f289e0953b8>
sage: elt.__hash__

[fchapoton]

comment:4

Looks similar to the problem here:

sage:  w = Word([0,1,1,0])
sage: type(w)
<class 'sage.combinat.words.word.FiniteWord_list'>
sage: w.__eq__
<method-wrapper '__eq__' of FiniteWord_list object at 0x7f840419ec78>
sage: w.__hash__

Maybe there is something to change in the way cython handles the __richcmp__ methods ?

[fchapoton]

Author: Frédéric Chapoton

[fchapoton]

Commit: dc1d704

[fchapoton]

New commits:

dc1d704

py3: hash for Cartesian product elements

[fchapoton]

Branch: u/chapoton/hash_cartesian

[sagetrac-git]

Branch pushed to git repo; I updated commit sha1. This was a forced push. New commits:

bc571fd

py3: hash for Cartesian product elements

[sagetrac-git]

Changed commit from dc1d704 to bc571fd

[tscrim]

Reviewer: Travis Scrimshaw

[tscrim]

comment:9

LGTM.

[dkrenn]

comment:10

Replying to @fchapoton:

indeed, hash does not exist, even if it appears in the tab completion: [...]

Fix LGTM, but can someone explain what is going on: The class ElementWrapper has a __hash__ defined; the class ElementWrapperCheckWrappedClass is derived from ElementWrapper, so there should be the same __hash__ used. Why does this not work (with Py3)?

[fchapoton]

comment:11

Probably because it redefines comparison __richcmp__, which itself is used by Cython to redefine __eq__.. just a guess..

[vbraun]

Changed branch from u/chapoton/hash_cartesian to bc571fd