Write 2to3 fixer for collections.abc imports

[opoplawski]

BPO	39482
Nosy	@benjaminp, @hroncok, @corona10, @tirkarthi
PRs	bpo-39482: Add a fixer to handling abstract base classes #18245

^{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 2020-04-25.08:10:29.533>
created_at = <Date 2020-01-29.04:03:13.021>
labels = ['type-feature', 'expert-2to3', '3.9']
title = 'Write 2to3 fixer for collections.abc imports'
updated_at = <Date 2020-04-25.08:10:29.532>
user = 'https://bugs.python.org/opoplawski'

bugs.python.org fields:

activity = <Date 2020-04-25.08:10:29.532>
actor = 'corona10'
assignee = 'none'
closed = True
closed_date = <Date 2020-04-25.08:10:29.533>
closer = 'corona10'
components = ['2to3 (2.x to 3.x conversion tool)']
creation = <Date 2020-01-29.04:03:13.021>
creator = 'opoplawski'
dependencies = []
files = []
hgrepos = []
issue_num = 39482
keywords = ['patch']
message_count = 2.0
messages = ['360936', '367264']
nosy_count = 5.0
nosy_names = ['benjamin.peterson', 'opoplawski', 'hroncok', 'corona10', 'xtreak']
pr_nums = ['18245']
priority = 'normal'
resolution = 'wont fix'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue39482'
versions = ['Python 3.9']

[opoplawski]

fail2ban currently relies on 2to3 for python 3 support. Build now fails with python 3.9:

Traceback (most recent call last):
  File "/builddir/build/BUILD/fail2ban-0.11.1/bin/fail2ban-testcases", line 61, in <module>
    tests = gatherTests(regexps, opts)
  File "./fail2ban/tests/utils.py", line 373, in gatherTests
    from . import clientreadertestcase
  File "./fail2ban/tests/clientreadertestcase.py", line 34, in <module>
    from ..client.jailreader import JailReader, extractOptions, splitWithOptions
  File "./fail2ban/client/jailreader.py", line 34, in <module>
    from .actionreader import ActionReader
  File "./fail2ban/client/actionreader.py", line 31, in <module>
    from ..server.action import CommandAction
  File "./fail2ban/server/action.py", line 33, in <module>
    from collections import MutableMapping
ImportError: cannot import name 'MutableMapping' from 'collections' (/usr/lib64/python3.9/collections/__init__.py)

[corona10]

Since https://bugs.python.org/issue40360 is now discussing lib2to3 deprecating.
The feature would not be needed.