collections: remove deprecated aliases to ABC classes

[vstinner]

BPO	37324
Nosy	@vstinner, @serhiy-storchaka, @yan12125, @hugovk, @tirkarthi
PRs	bpo-37324: Remove ABC aliases from collections #14171 bpo-37324: Remove ABC aliases from collections #23754
Superseder	bpo-25988: collections.abc.Indexable

^{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 2019-10-07.13:20:44.080>
created_at = <Date 2019-06-17.20:38:32.149>
labels = ['library', '3.9']
title = 'collections: remove deprecated aliases to ABC classes'
updated_at = <Date 2021-01-12.23:16:45.583>
user = 'https://github.com/vstinner'

bugs.python.org fields:

activity = <Date 2021-01-12.23:16:45.583>
actor = 'vstinner'
assignee = 'none'
closed = True
closed_date = <Date 2019-10-07.13:20:44.080>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2019-06-17.20:38:32.149>
creator = 'vstinner'
dependencies = []
files = []
hgrepos = []
issue_num = 37324
keywords = ['patch']
message_count = 8.0
messages = ['345905', '345906', '345908', '345923', '348011', '348424', '354092', '384981']
nosy_count = 5.0
nosy_names = ['vstinner', 'serhiy.storchaka', 'yan12125', 'hugovk', 'xtreak']
pr_nums = ['14171', '23754']
priority = 'normal'
resolution = 'duplicate'
stage = 'resolved'
status = 'closed'
superseder = '25988'
type = None
url = 'https://bugs.python.org/issue37324'
versions = ['Python 3.9']

[vstinner]

Extract of collections documentation:
https://docs.python.org/dev/library/collections.html

"Deprecated since version 3.3, will be removed in version 3.9: Moved Collections Abstract Base Classes to the collections.abc module. For backwards compatibility, they continue to be visible in this module through Python 3.8."

Attached PR removes these aliases.

[vstinner]

pip is broken by this change, causing test_venv to fail: html5lib still uses collections to get ABC.

FAIL: test_with_pip (test.test_venv.EnsurePipTest)
----------------------------------------------------------------------

Traceback (most recent call last):
  File "/home/vstinner/prog/python/master/Lib/test/test_venv.py", line 407, in do_test_with_pip
    self.run_with_capture(venv.create, self.env_dir,
  File "/home/vstinner/prog/python/master/Lib/test/test_venv.py", line 69, in run_with_capture
    func(*args, **kwargs)
subprocess.CalledProcessError: Command '['/tmp/tmpkxga42lx/bin/python', '-Im', 'ensurepip', '--upgrade', '--default-pip']' returned non-zero exit status 1.

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/vstinner/prog/python/master/Lib/test/test_venv.py", line 466, in test_with_pip
    self.do_test_with_pip(False)
  File "/home/vstinner/prog/python/master/Lib/test/test_venv.py", line 415, in do_test_with_pip
    self.fail(msg.format(exc, details))
AssertionError: Command '['/tmp/tmpkxga42lx/bin/python', '-Im', 'ensurepip', '--upgrade', '--default-pip']' returned non-zero exit status 1.

**Subprocess Output**
/tmp/tmpwhk_ss_e/pip-19.0.3-py2.py3-none-any.whl/pip/_vendor/pyparsing.py:3068: SyntaxWarning: invalid escape sequence \w
/tmp/tmpwhk_ss_e/pip-19.0.3-py2.py3-none-any.whl/pip/_vendor/pyparsing.py:3068: SyntaxWarning: invalid escape sequence \w
Traceback (most recent call last):
  File "/home/vstinner/prog/python/master/Lib/runpy.py", line 192, in _run_module_as_main
    return _run_code(code, main_globals, None,
  File "/home/vstinner/prog/python/master/Lib/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/home/vstinner/prog/python/master/Lib/ensurepip/__main__.py", line 5, in <module>
    sys.exit(ensurepip._main())
  File "/home/vstinner/prog/python/master/Lib/ensurepip/__init__.py", line 198, in _main
    return _bootstrap(
  File "/home/vstinner/prog/python/master/Lib/ensurepip/__init__.py", line 117, in _bootstrap
    return _run_pip(args + [p[0] for p in _PROJECTS], additional_paths)
  File "/home/vstinner/prog/python/master/Lib/ensurepip/__init__.py", line 27, in _run_pip
    import pip._internal
  File "<frozen zipimport>", line 259, in load_module
  File "/tmp/tmpwhk_ss_e/pip-19.0.3-py2.py3-none-any.whl/pip/_internal/__init__.py", line 40, in <module>
  File "<frozen zipimport>", line 259, in load_module
  File "/tmp/tmpwhk_ss_e/pip-19.0.3-py2.py3-none-any.whl/pip/_internal/cli/autocompletion.py", line 8, in <module>
  File "<frozen zipimport>", line 259, in load_module
  File "/tmp/tmpwhk_ss_e/pip-19.0.3-py2.py3-none-any.whl/pip/_internal/cli/main_parser.py", line 12, in <module>
  File "<frozen zipimport>", line 259, in load_module
  File "/tmp/tmpwhk_ss_e/pip-19.0.3-py2.py3-none-any.whl/pip/_internal/commands/__init__.py", line 6, in <module>
  File "<frozen zipimport>", line 259, in load_module
  File "/tmp/tmpwhk_ss_e/pip-19.0.3-py2.py3-none-any.whl/pip/_internal/commands/completion.py", line 6, in <module>
  File "<frozen zipimport>", line 259, in load_module
  File "/tmp/tmpwhk_ss_e/pip-19.0.3-py2.py3-none-any.whl/pip/_internal/cli/base_command.py", line 25, in <module>
  File "<frozen zipimport>", line 259, in load_module
  File "/tmp/tmpwhk_ss_e/pip-19.0.3-py2.py3-none-any.whl/pip/_internal/index.py", line 14, in <module>
  File "<frozen zipimport>", line 259, in load_module
  File "/tmp/tmpwhk_ss_e/pip-19.0.3-py2.py3-none-any.whl/pip/_vendor/html5lib/__init__.py", line 25, in <module>
  File "<frozen zipimport>", line 259, in load_module
  File "/tmp/tmpwhk_ss_e/pip-19.0.3-py2.py3-none-any.whl/pip/_vendor/html5lib/html5parser.py", line 8, in <module>
  File "<frozen zipimport>", line 259, in load_module
  File "/tmp/tmpwhk_ss_e/pip-19.0.3-py2.py3-none-any.whl/pip/_vendor/html5lib/_tokenizer.py", line 16, in <module>
  File "<frozen zipimport>", line 259, in load_module
  File "/tmp/tmpwhk_ss_e/pip-19.0.3-py2.py3-none-any.whl/pip/_vendor/html5lib/_trie/__init__.py", line 3, in <module>
  File "<frozen zipimport>", line 259, in load_module
  File "/tmp/tmpwhk_ss_e/pip-19.0.3-py2.py3-none-any.whl/pip/_vendor/html5lib/_trie/py.py", line 6, in <module>
  File "<frozen zipimport>", line 259, in load_module
  File "/tmp/tmpwhk_ss_e/pip-19.0.3-py2.py3-none-any.whl/pip/_vendor/html5lib/_trie/_base.py", line 3, in <module>
ImportError: cannot import name 'Mapping' from 'collections' (/home/vstinner/prog/python/master/Lib/collections/__init__.py)

[vstinner]

html5lib has already been fixed:
https://github.com/vstinner/html5lib-python/commit/4f9235752cea29c5a31721440578b430823a1e69

But latest html5lib release was version 1.0.1 at... Dec 7, 2017 :-(

Paul Ganssle requested a new html5lib release... to fix the collections warning :-)
html5lib/html5lib-python#419

[vstinner]

Oh. I wasn't aware of the previous attempt: #10596 there is a long discussion there. The blocker issue was also html5lib.

[vstinner]

Right now (pip 19.1.1?), "./python -m venv env" still fails because of html5lib/_trie/py.py. There is still no activitiy on the request to get a new release:
html5lib/html5lib-python#419

[yan12125]

In CPython commit 5380def, bundled pip is updated to 19.2.1, and since pip 19.2 an html5lib patch is backported [1] to "prefer importing from collections.abc instead of collections" [2]. I believe #10596 can be revisited now.

[1] pypa/pip@ef7ca14
[2] pypa/pip@3d6bb3a

[tirkarthi]

I think this can be closed since https://bugs.python.org/issue25988 has the PR merged.

[vstinner]

New changeset c47c78b by Hugo van Kemenade in branch 'master':
bpo-37324: Remove ABC aliases from collections (GH-23754)
c47c78b