py3: implement PolyDict.__hash__

[embray]

This type needs to have an explicit __hash__ implementation for Python 3.

Although its underlying data structure is a mutable dict, it's not intended to be mutated and the API generally disallows this (it still might be better if it used an immutable dict).

Component: python3

Author: Erik Bray

Branch/Commit: 4f5e114

Reviewer: Frédéric Chapoton

Issue created by migration from https://trac.sagemath.org/ticket/24761

[embray]

Dependencies: #24760

[embray]

Changed dependencies from #24760 to #24759

[tscrim]

comment:3

Instead of sorting the output, I would use a frozenset since that is more inline with the mathematical interpretation. I also feel like that (in general) would be faster than sorting, but I haven't tested. Thoughts?

[jdemeyer]

comment:4

Just one detail: type(x) is faster than x.__class__ in Cython code.

[fchapoton]

comment:5

does not apply

[embray]

comment:6

Replying to @tscrim:

Instead of sorting the output, I would use a frozenset since that is more inline with the mathematical interpretation. I also feel like that (in general) would be faster than sorting, but I haven't tested. Thoughts?

Yes, I think you have a point there. I'll try it out.

[embray]

comment:7

Replying to @jdemeyer:

Just one detail: type(x) is faster than x.__class__ in Cython code.

Interesting--I'd have just assumed they would optimize that, but I guess technically you can't since many objects' .__class__ can be overridden. We're certainly not concerned with that here.

[jdemeyer]

comment:8

Replying to @embray:

Interesting--I'd have just assumed they would optimize that, but I guess technically you can't since many objects' .__class__ can be overridden.

Indeed. Cython really wants to be Python-compatible. type() is a built-in function, so Cython knows exactly what it does. But .__class__ is just an attribute that a custom (meta?)class can override.

This also explains why you shouldn't do from six.moves import range in Cython code: instead of a known builtin, you get a random Python object that Cython cannot do anything with.

[sagetrac-git]

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

43d9234	fixing doctests
f2ea845	Merge branch 'public/polydict-sort-repr' in 8.2.b6
4f5e114	Implement PolyDict.__hash__

[sagetrac-git]

Changed commit from a515c54 to 4f5e114

[embray]

comment:10

Rebased and incorporated minor review comments.

---

New commits:

43d9234	fixing doctests
f2ea845	Merge branch 'public/polydict-sort-repr' in 8.2.b6
4f5e114	Implement PolyDict.__hash__

[fchapoton]

Changed dependencies from #24759 to none

[fchapoton]

Reviewer: Frédéric Chapoton

[fchapoton]

comment:12

ok

[vbraun]

Changed branch from u/embray/polydict-hash to 4f5e114