time.tzname returns empty string on Windows if default codepage is a Unicode codepage

[paulmon]

BPO	36779
Nosy	@pfmoore, @vstinner, @tjguk, @zware, @zooba, @matrixise, @miss-islington, @paulmon
PRs	bpo-36779: time.tzname returns empty string on Windows if default cod… #13073 [3.8] bpo-36779: time.tzname returns empty string on Windows if default cod… (GH-13073) #14032 [3.7] bpo-36779: time.tzname returns empty string on Windows if default cod… (GH-13073) #14057

^{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 2019-06-12.23:54:23.769>
created_at = <Date 2019-05-03.00:45:22.319>
labels = ['3.8', 'type-bug', '3.7', 'OS-windows']
title = 'time.tzname returns empty string on Windows if default codepage is a Unicode codepage'
updated_at = <Date 2021-03-08.18:25:28.786>
user = 'https://github.com/paulmon'

bugs.python.org fields:

activity = <Date 2021-03-08.18:25:28.786>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2019-06-12.23:54:23.769>
closer = 'Paul Monson'
components = ['Windows']
creation = <Date 2019-05-03.00:45:22.319>
creator = 'Paul Monson'
dependencies = []
files = []
hgrepos = []
issue_num = 36779
keywords = ['patch']
message_count = 5.0
messages = ['341318', '343148', '345426', '345515', '345517']
nosy_count = 8.0
nosy_names = ['paul.moore', 'vstinner', 'tim.golden', 'zach.ware', 'steve.dower', 'matrixise', 'miss-islington', 'Paul Monson']
pr_nums = ['13073', '14032', '14057']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue36779'
versions = ['Python 3.7', 'Python 3.8']

[paulmon]

Need to work around a CRT bug in the use of _tzset() + _tzname[]
Calling setlocale(LC_CTYPE, "") on a system where GetACP() returns CP_UTF8 results in empty strings in _tzname[].
This causes time.tzname to be an empty string.
I have reported the bug.

One possible workaround is to temporarily change the locale by calling setlocale(LC_CTYPE, "C") before calling _tzset and restore the current locale after if the GetACP() == CP_UTF8 or CP_UTF7

[matrixise]

Hi Paul,

I have added your PR at this issue, it was assigned to another bpo issue.

[miss-islington]

New changeset b4c7def by Miss Islington (bot) (Paul Monson) in branch 'master':
bpo-36779: time.tzname returns empty string on Windows if default cod… (GH-13073)
b4c7def

[vstinner]

New changeset 0a9baec by Victor Stinner (Miss Islington (bot)) in branch '3.8':
bpo-36779: time.tzname returns empty string on Windows if default cod… (GH-13073) (GH-14032)
0a9baec

[miss-islington]

New changeset 6a433f5 by Miss Islington (bot) in branch '3.7':
bpo-36779: time.tzname returns empty string on Windows if default cod… (GH-13073)
6a433f5