Add migration step for DictMixin -> collections.MutableMapping

[tiran]

BPO	2012
Nosy	@rhettinger, @ncoghlan, @tiran
Superseder	bpo-2876: Write UserDict fixer for 2to3

^{Note: these values reflect the state of the issue at the time it was migrated and might not reflect the current state.}

Show more details

GitHub fields:

assignee = None
closed_at = <Date 2008-08-21.22:24:06.292>
created_at = <Date 2008-02-05.01:32:30.677>
labels = ['type-feature', 'expert-2to3']
title = 'Add migration step for DictMixin -> collections.MutableMapping'
updated_at = <Date 2008-08-21.22:24:06.292>
user = 'https://github.com/tiran'

bugs.python.org fields:

activity = <Date 2008-08-21.22:24:06.292>
actor = 'benjamin.peterson'
assignee = 'collinwinter'
closed = True
closed_date = <Date 2008-08-21.22:24:06.292>
closer = 'benjamin.peterson'
components = ['2to3 (2.x to 3.x conversion tool)']
creation = <Date 2008-02-05.01:32:30.677>
creator = 'christian.heimes'
dependencies = []
files = []
hgrepos = []
issue_num = 2012
keywords = []
message_count = 4.0
messages = ['62058', '62063', '62221', '62234']
nosy_count = 4.0
nosy_names = ['collinwinter', 'rhettinger', 'ncoghlan', 'christian.heimes']
pr_nums = []
priority = 'normal'
resolution = 'duplicate'
stage = None
status = 'closed'
superseder = '2876'
type = 'enhancement'
url = 'https://bugs.python.org/issue2012'
versions = ['Python 2.6', 'Python 3.0']

[tiran]

See r60577

[rhettinger]

The difference is the underlying methods. DictMixin depended on
getitem, setitem, delitem, and keys. MutableMapping doesn't need keys
but wants __iter__ and __len__. Also, DictMixin did not insist on all
of those being present, while MutableMapping won't let you skip any
(with delitem being the one most likely omitted).

[ncoghlan]

Perhaps the best we can do is a warning from the DictMixin constructor
in 2.6 when the -3 flag is specified?

[rhettinger]

We should hold off on this one for a bit until I can get feedback on
whether UserDict, UserString, and UserList should all be in the same
place (in the own modules or rolled into collections).