uuid.UUID objects can't be unpickled in older Python versions (<3.7)

[taleinat]

BPO	34621
Nosy	@taleinat, @serhiy-storchaka
PRs	[3.7] bpo-34621: fix uuid.UUID (un)pickling compatbility with older Python versions (<3.7) #9133 [3.7] bpo-34621: backwards-compatible pickle UUID with is_safe=unknown #14834

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

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GitHub fields:

assignee = None
closed_at = <Date 2018-09-10.15:47:50.435>
created_at = <Date 2018-09-10.12:16:57.781>
labels = ['3.7', 'type-bug', 'library']
title = "uuid.UUID objects can't be unpickled in older Python versions (<3.7)"
updated_at = <Date 2019-08-04.19:30:11.204>
user = 'https://github.com/taleinat'

bugs.python.org fields:

activity = <Date 2019-08-04.19:30:11.204>
actor = 'taleinat'
assignee = 'none'
closed = True
closed_date = <Date 2018-09-10.15:47:50.435>
closer = 'taleinat'
components = ['Library (Lib)']
creation = <Date 2018-09-10.12:16:57.781>
creator = 'taleinat'
dependencies = []
files = []
hgrepos = []
issue_num = 34621
keywords = ['patch']
message_count = 4.0
messages = ['324919', '324927', '348997', '348999']
nosy_count = 2.0
nosy_names = ['taleinat', 'serhiy.storchaka']
pr_nums = ['9133', '14834']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue34621'
versions = ['Python 3.7']

[taleinat]

This affects only 3.7, where the new SafeUUID enum was introduced.

This was fixed on the master branch (3.8) while implementing bpo-30977.

Fixing this should simply require defining similar __getstate__ and __setstate__ methods as in 3.8.

[taleinat]

New changeset d53f1ca by Tal Einat in branch '3.7':
[3.7] bpo-34621: fix uuid.UUID (un)pickling compatbility with older Python versions (<3.7) (GH-9133)
d53f1ca

[taleinat]

New changeset a2ea944 by Tal Einat in branch '3.7':
[3.7] bpo-34621: backwards-compatible pickle UUID with is_safe=unknown (GH-14834)
a2ea944

[taleinat]

Note that the original fix, in PR #53379, contained a bug: UUID objects with is_safe set to SafeUUID.unknown would cause an exception if unpickled with Python <3.7.

This was reported by Thomas Wiebe in a comment to a commit in that PR:
d53f1ca#commitcomment-31396021

This is now fixed, see PR #59039.