Enhance swap_attr() and swap_item() in test.support

[serhiy-storchaka]

BPO	30197
Nosy	@vstinner, @ezio-melotti, @voidspace, @serhiy-storchaka
PRs	bpo-30197: Enhance functions swap_attr() and swap_item() in test.support. #1341 [3.6] bpo-30197: Enhance functions swap_attr() and swap_item() in tes… #1345 [3.5] bpo-30197: Enhance functions swap_attr() and swap_item() in test.support. (#1341) #1346 [2.7] bpo-30197: Enhance swap_attr() and backport swap_item() in test.test_support. (#1341) #1347

^{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 2017-04-28.17:07:22.174>
created_at = <Date 2017-04-28.11:06:00.937>
labels = ['3.7', 'type-feature', 'tests']
title = 'Enhance swap_attr() and swap_item() in test.support'
updated_at = <Date 2020-10-06.10:48:50.555>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2020-10-06.10:48:50.555>
actor = 'wburchill7'
assignee = 'none'
closed = True
closed_date = <Date 2017-04-28.17:07:22.174>
closer = 'serhiy.storchaka'
components = ['Tests']
creation = <Date 2017-04-28.11:06:00.937>
creator = 'serhiy.storchaka'
dependencies = []
files = []
hgrepos = []
issue_num = 30197
keywords = []
message_count = 6.0
messages = ['292527', '292536', '292539', '292541', '292542', '378109']
nosy_count = 5.0
nosy_names = ['vstinner', 'ezio.melotti', 'michael.foord', 'serhiy.storchaka', 'wburchill7']
pr_nums = ['1341', '1345', '1346', '1347']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue30197'
versions = ['Python 2.7', 'Python 3.5', 'Python 3.6', 'Python 3.7']

[serhiy-storchaka]

Proposed patch adds two features to functions swap_attr() and swap_item() in the test.support module.

1. They now work (rather than failing in __exit__) when delete the attribute or item inside the with block. There were several cases when I refused to use these functions instead of manually coded try/finally due to lack of this feature.

2. The original value of the attribute or item can be assigned to the target of "as" in the with statement. This can save a line of the code in some cases.

[vstinner]

New changeset d1a1def by Victor Stinner (Serhiy Storchaka) in branch 'master':
bpo-30197: Enhance functions swap_attr() and swap_item() in test.support. (bpo-1341)
d1a1def

[serhiy-storchaka]

New changeset 712114b by Serhiy Storchaka in branch '3.6':
[3.6] bpo-30197: Enhance functions swap_attr() and swap_item() in test.support. (GH-1341) (bpo-1345)
712114b

[serhiy-storchaka]

New changeset 910ba93 by Serhiy Storchaka in branch '3.5':
[3.5] bpo-30197: Enhance functions swap_attr() and swap_item() in test.support. (bpo-1341) (bpo-1346)
910ba93

[serhiy-storchaka]

New changeset 941ea53 by Serhiy Storchaka in branch '2.7':
[2.7] bpo-30197: Enhance swap_attr() and backport swap_item() in test.test_support. (bpo-1341) (bpo-1347)
941ea53

[wburchill7]

Thought I'd send