Minor repr error in typing.TypeVar.__ror__()

[larryhastings]

BPO	43772
Nosy	@gvanrossum, @larryhastings, @ilevkivskyi, @JelleZijlstra, @Fidget-Spinner
PRs	bpo-43772: fix TypeVar.__ror__ #25339

^{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 2021-04-11.03:00:19.295>
created_at = <Date 2021-04-08.11:09:29.646>
labels = ['type-bug', 'library', '3.10']
title = 'Minor repr error in typing.TypeVar.__ror__()'
updated_at = <Date 2021-04-11.03:00:19.295>
user = 'https://github.com/larryhastings'

bugs.python.org fields:

activity = <Date 2021-04-11.03:00:19.295>
actor = 'gvanrossum'
assignee = 'none'
closed = True
closed_date = <Date 2021-04-11.03:00:19.295>
closer = 'gvanrossum'
components = ['Library (Lib)']
creation = <Date 2021-04-08.11:09:29.646>
creator = 'larry'
dependencies = []
files = []
hgrepos = []
issue_num = 43772
keywords = ['patch']
message_count = 3.0
messages = ['390524', '390540', '390764']
nosy_count = 5.0
nosy_names = ['gvanrossum', 'larry', 'levkivskyi', 'JelleZijlstra', 'kj']
pr_nums = ['25339']
priority = 'low'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue43772'
versions = ['Python 3.10']

[larryhastings]

The implementation of the | operator for TypeVar objects is as follows:

    def __or__(self, right):
        return Union[self, right]

    def __ror__(self, right):
        return Union[self, right]

I think the implementation of __ror__ is ever-so-slightly inaccurate. Shouldn't it be this?

    def __ror__(self, left):
        return Union[left, self]

I assume this wouldn't affect runtime behavior, as unions are sets and are presumably unordered. The only observable difference should be in the repr() (and only then if both are non-None), as this reverses the elements. The repr for Union does preserve the order of the elements it contains, so it's visible to the user there.

[gvanrossum]

Yes.--
--Guido (mobile)

[gvanrossum]

New changeset 9045919 by Jelle Zijlstra in branch 'master':
bpo-43772: Fix TypeVar.__ror__ (GH-25339)
9045919