Disable coerce_c_locale and utf8_mode by default in _PyPreConfig?

[vstinner]

BPO	36443
Nosy	@ncoghlan, @vstinner
PRs	bpo-36443: Disable C locale coercion and UTF-8 Mode by default #12589

^{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 2019-03-27.17:30:10.749>
created_at = <Date 2019-03-26.23:04:10.529>
labels = ['interpreter-core', '3.8']
title = 'Disable coerce_c_locale and utf8_mode by default in _PyPreConfig?'
updated_at = <Date 2019-03-27.17:30:10.748>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2019-03-27.17:30:10.748>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2019-03-27.17:30:10.749>
closer = 'vstinner'
components = ['Interpreter Core']
creation = <Date 2019-03-26.23:04:10.529>
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 36443
keywords = ['patch']
message_count = 3.0
messages = ['338922', '338978', '338980']
nosy_count = 2.0
nosy_names = ['ncoghlan', 'vstinner']
pr_nums = ['12589']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue36443'
versions = ['Python 3.8']

[vstinner]

bpo-36301 created a very strict separated between Python initialization and a new "pre-initialization" which is responsible to configure encodings and memory allocators.

Nick Coghlan proposed to disable UTF-8 Mode and C locale coercion by default in the pre-initialization, so the LC_CTYPE locale is not coerced by Python when it's embedded in an application.

Maybe the UTF-8 Mode can be automatically enabled (depending on the LC_CTYPE locale), but not the C locale coercion?

This issue is related to bpo-36202: Calling Py_DecodeLocale() before _PyPreConfig_Write() can produce mojibake.

[vstinner]

New changeset d929f18 by Victor Stinner in branch 'master':
bpo-36443: Disable C locale coercion and UTF-8 Mode by default (GH-12589)
d929f18

[vstinner]

Done. I close the issue.