Make dict views copyable

[serhiy-storchaka]

BPO	27252
Nosy	@gvanrossum, @rhettinger, @serhiy-storchaka
Files	dict_views_copy.patch

^{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 2016-06-26.21:41:58.364>
created_at = <Date 2016-06-07.16:27:29.648>
labels = ['type-feature', 'library']
title = 'Make dict views copyable'
updated_at = <Date 2016-06-26.21:41:58.363>
user = 'https://github.com/serhiy-storchaka'

bugs.python.org fields:

activity = <Date 2016-06-26.21:41:58.363>
actor = 'serhiy.storchaka'
assignee = 'none'
closed = True
closed_date = <Date 2016-06-26.21:41:58.364>
closer = 'serhiy.storchaka'
components = ['Library (Lib)']
creation = <Date 2016-06-07.16:27:29.648>
creator = 'serhiy.storchaka'
dependencies = []
files = ['43280']
hgrepos = []
issue_num = 27252
keywords = ['patch']
message_count = 5.0
messages = ['267701', '267703', '267713', '267717', '267756']
nosy_count = 3.0
nosy_names = ['gvanrossum', 'rhettinger', 'serhiy.storchaka']
pr_nums = []
priority = 'normal'
resolution = 'rejected'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue27252'
versions = ['Python 3.6']

[serhiy-storchaka]

Proposed patch adds support of dict views in the copy module.

Since dict views are immutable, copy.copy() just returns the same object.

copy.deepcopy() returns a frozenset for the dict_keys object, a tuple for the dict_values object, and a dict_items object for the dict_items object. Only needed data is copied (keys for dict_keys, values for dict_values).

[gvanrossum]

I'm still not clear about the use case -- have you heard from people who had to work around the current situation? Use of the copy module is often a code smell in my experience, so I don't want to encourage it.

[serhiy-storchaka]

I didn't encounter this.

[rhettinger]

I think we should stop adding features like this without actual user requests and real use cases to show necessity and to inform the design.

[rhettinger]

See also: http://bugs.python.org/issue27253