frozenset.__hash__ vs. Set._hash

[Prometheus3375]

BPO	44704
Nosy	@rhettinger, @miss-islington, @sweeneyde, @Prometheus3375
PRs	bpo-44704: Make Set._hash consistent with frozenset.__hash__ #27281 [3.10] bpo-44704: Make Set._hash consistent with frozenset.__hash__ (GH-27281) #27282 [3.9] bpo-44704: Make Set._hash consistent with frozenset.__hash__ (GH-27281) #27283

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

Show more details

GitHub fields:

assignee = None
closed_at = <Date 2021-07-21.23:59:44.967>
created_at = <Date 2021-07-21.21:32:14.420>
labels = ['type-bug', 'library', '3.9']
title = 'frozenset.__hash__ vs. Set._hash'
updated_at = <Date 2021-07-22.00:23:47.837>
user = 'https://github.com/Prometheus3375'

bugs.python.org fields:

activity = <Date 2021-07-22.00:23:47.837>
actor = 'rhettinger'
assignee = 'none'
closed = True
closed_date = <Date 2021-07-21.23:59:44.967>
closer = 'rhettinger'
components = ['Library (Lib)']
creation = <Date 2021-07-21.21:32:14.420>
creator = 'Prometheus3375'
dependencies = []
files = []
hgrepos = []
issue_num = 44704
keywords = ['patch']
message_count = 4.0
messages = ['397963', '397968', '397970', '397972', '397973']
nosy_count = 4.0
nosy_names = ['rhettinger', 'miss-islington', 'Dennis Sweeney', 'Prometheus3375']
pr_nums = ['27281', '27282', '27283']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue44704'
versions = ['Python 3.9']

[Prometheus3375]

In docstring of Set._hash in _collections_abc.py is written:
"We match the algorithm used by the built-in frozenset type."

But
>>> s = frozenset({i for i in range(10)})
>>> hash(s)
3895031357313128696
>>> Set._hash(s)
3914343279946282847

Looks like Set._hash is different.

[sweeneyde]

I opened a PR. It looks like frozenset.__hash__ changed in #49444 and #49485, but Set._hash wasn't updated accordingly.

[rhettinger]

New changeset c878f5d by Dennis Sweeney in branch 'main':
bpo-44704: Make Set._hash consistent with frozenset.__hash__ (GH-27281)
c878f5d

[rhettinger]

New changeset e0ef816 by Miss Islington (bot) in branch '3.9':
bpo-44704: Make Set._hash consistent with frozenset.__hash__ (GH-27281) (GH-27283)
e0ef816

[rhettinger]

New changeset 4194f14 by Miss Islington (bot) in branch '3.10':
bpo-44704: Make Set._hash consistent with frozenset.__hash__ (GH-27281) (GH-27282)
4194f14