Port the standard library to PEP 489 multiphase initialization

[Dormouse759]

BPO	31862
Nosy	@ncoghlan, @vstinner, @encukou, @Dormouse759
PRs	bpo-31862: Port binascii to PEP 489 multiphase initialization #4108
Superseder	bpo-1635741: Py_Finalize() doesn't clear all Python objects at exit

^{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 2020-09-07.13:55:38.744>
created_at = <Date 2017-10-24.15:08:56.007>
labels = ['extension-modules', 'type-feature', '3.7']
title = 'Port the standard library to PEP 489 multiphase initialization'
updated_at = <Date 2020-09-07.13:55:38.743>
user = 'https://github.com/Dormouse759'

bugs.python.org fields:

activity = <Date 2020-09-07.13:55:38.743>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2020-09-07.13:55:38.744>
closer = 'vstinner'
components = ['Extension Modules']
creation = <Date 2017-10-24.15:08:56.007>
creator = 'Dormouse759'
dependencies = []
files = []
hgrepos = []
issue_num = 31862
keywords = ['patch']
message_count = 6.0
messages = ['304914', '304916', '343182', '376487', '376488', '376489']
nosy_count = 4.0
nosy_names = ['ncoghlan', 'vstinner', 'petr.viktorin', 'Dormouse759']
pr_nums = ['4108']
priority = 'normal'
resolution = 'duplicate'
stage = 'resolved'
status = 'closed'
superseder = '1635741'
type = 'enhancement'
url = 'https://bugs.python.org/issue31862'
versions = ['Python 3.7']

[Dormouse759]

PEP-489 introduced multiphase initialization of extension and built-in modules.
Now, almost no module in the standard library supports this feature. This should be improved to prepare Python for better testing of subinterpreters.

Many benefits of PEP-489 don't apply to stdlib modules. However, the PEP effectively says that by using multi-phase init, the module author "promises" that the module is "subinterpreter-friendly" 0. So, when porting, each module should be checked that it e.g. doesn't use mutable process-global state.

I'd like to port stdlib to multi-phase init, starting with the easier modules, to:
- get familiar with contributing to CPython,
- check and track which modules are already "subinterpreter-friendly", and
- figure out how and where PEP-489 is lacking (beyond what is discussed in the PEP itself).

[encukou]

FWIW, Marcel is an intern in my team, tasked to learn CPython internals by trying to improve subinterpreter support. If I don't comment on his issues it's because we discussed privately beforehand.

[encukou]

New changeset 33e71e0 by Petr Viktorin (Marcel Plch) in branch 'master':
bpo-31862: Port binascii to PEP-489 multiphase initialization (GH-4108)
33e71e0

[vstinner]

I marked bpo-15681 "PEP-3121 refactoring applied to binascii module" as a duplicate of this issue.

[vstinner]

See also bpo-1635741 "Py_Finalize() doesn't clear all Python objects at exit": many extension modules have been ported to multi-phase initialization API (PEP-489) there.

[vstinner]

I prefer to track the work in a single issue. Even if bpo-1635741 contains many unrelated changes, I prefer to continue to use bpo-1635741 to track the work on "porting the standard library to PEP-489 multiphase initialization".