Deprecate various things in importlib thanks to PEP 451

[brettcannon]

BPO	19713
Nosy	@brettcannon, @ncoghlan, @larryhastings, @encukou, @ericsnowcurrently, @serhiy-storchaka
Dependencies	bpo-19703: Update pydoc to PEP 451 bpo-19708: Check pkgutil for anything missing for PEP 451
Files	issue19713-importlib-docs.diff issue19713-switch-to-new-api.diff issue19713-more-API-adjustments.diff issue19713-deprecation-warnings.diff

^{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 = 'https://github.com/ericsnowcurrently'
closed_at = <Date 2014-01-07.03:55:08.288>
created_at = <Date 2013-11-22.16:50:06.976>
labels = []
title = 'Deprecate various things in importlib thanks to PEP 451'
updated_at = <Date 2015-07-11.18:52:29.614>
user = 'https://github.com/brettcannon'

bugs.python.org fields:

activity = <Date 2015-07-11.18:52:29.614>
actor = 'petr.viktorin'
assignee = 'eric.snow'
closed = True
closed_date = <Date 2014-01-07.03:55:08.288>
closer = 'eric.snow'
components = []
creation = <Date 2013-11-22.16:50:06.976>
creator = 'brett.cannon'
dependencies = ['19703', '19708']
files = ['33088', '33300', '33314', '33315']
hgrepos = []
issue_num = 19713
keywords = ['patch']
message_count = 38.0
messages = ['203807', '203808', '203824', '203920', '203933', '204044', '204163', '204736', '205886', '206402', '206404', '206405', '206407', '206410', '206411', '206440', '206583', '206599', '206654', '206658', '206660', '207214', '207314', '207318', '207322', '207324', '207325', '207327', '207359', '207360', '207361', '207367', '207501', '207503', '207504', '207567', '207674', '207675']
nosy_count = 8.0
nosy_names = ['brett.cannon', 'ncoghlan', 'larry', 'Arfrever', 'petr.viktorin', 'python-dev', 'eric.snow', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue19713'
versions = ['Python 3.4']

[brettcannon]

http://bugs.python.org/msg202659

[brettcannon]

Also msg202663 and msg202664

[ericsnowcurrently]

See http://www.python.org/dev/peps/pep-0451/#deprecations.

[ncoghlan]

Keep in mind we figured out post-PEP acceptance that there are still a
couple of obscure use cases that need the old loader API, so we may want to
keep that around as a "power user" mode rather than deprecating it (either
forever or until a replacement is defined in 3.5)

[ericsnowcurrently]

It's definitely worth it to be more explicit. (Brett had referenced msg202663.) When I get some time I'll update this ticket with a list of the specific deprecation items.

[brettcannon]

I do not think we should keep the old APIs around forever, so either we don't care about the obscure use cases or figure out a way to support them.

[ncoghlan]

I think we should definitely support them, I just haven't thought of a way
to do that yet which is cleaner than the status quo (it's only the loader
part of the API that isn't fully covered - the rest of the legacy APIs can
be deprecated happily). I may come up with an idea once we start work on
migrating extension module loading in 3.5.

[brettcannon]

To add another point about load_module(), I just had to rip out exec_module() for Python 3.4 as working around _imp.init_builtin() and _imp.load_dynamic() are going to need to be done hand-in-hand. So load_module() should probably get documented as deprecated and nothing more. Everything else can be hard deprecated.

[ericsnowcurrently]

Here's a patch for the deprecations (and API additions) in the importlib docs.

[python-dev]

New changeset 2c27c0e5bc50 by Eric Snow in branch 'default':
Issue bpo-19713: Update importlib docs for module spec changes, including deprecations.
http://hg.python.org/cpython/rev/2c27c0e5bc50

New changeset b78de8029606 by Eric Snow in branch 'default':
Issue bpo-19713: Fix mistakes in the import page of language reference.
http://hg.python.org/cpython/rev/b78de8029606

[ericsnowcurrently]

The doc deprecations should now be complete.

[ericsnowcurrently]

P.S. changeset b78de8029606 should have referred to bpo-19710.

[ericsnowcurrently]

Here's a patch that simply adds all the deprecation warnings. It does not include any effort to silence the zillion warnings that happen when the test suite is run with -Wall. I plan on addressing all those when I have some time. That will be a matter of refactoring tests or stdlib modules to not use deprecated APIs.

In cases when the warnings happen due to BuiltinImporter.load_module() or ExtensionFileLoader.load_module(), I'll need to silence the warnings in the tests.

2 questions:

• Could I push this changeset (after a few fixes) before adding in all the refactors, doing those separately?
• Could we special-case BuiltinImporter and ExtensionFileLoader in _SpecMethods._load_backward_compatible() so that they don't cause a warning? I know we've also talked about skipping the deprecation warning entirely for load_module()...

There are also several places in _bootstrap where a method (A) may raise a warning and a method it calls (B) may raise a similar warning. Would there be any probably with silencing the deprecation warning coming out of the called method (B)?

[serhiy-storchaka]

Could you please use correct stacklevel, such that warnings will point to places where deprecated function used, not where they are defined?

[ericsnowcurrently]

I'd meant to do that. I'll update the patch when I have a chance.