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Dict order is now guaranteed, so add tests and doc for it #76518

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rhettinger opened this issue Dec 15, 2017 · 11 comments
Closed

Dict order is now guaranteed, so add tests and doc for it #76518

rhettinger opened this issue Dec 15, 2017 · 11 comments
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3.7 (EOL) end of life 3.8 only security fixes tests Tests in the Lib/test dir

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@rhettinger
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BPO 32337
Nosy @rhettinger, @ned-deily, @stevendaprano, @methane, @zhangyangyu, @shangdahao, @miss-islington
PRs
  • bpo-32337: Update tutorial and documentation related with dict order. #4973
  • [3.7] bpo-32337: Update documentats about dict order (GH-4973) #6368
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    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 2018-04-04.17:36:05.905>
created_at = <Date 2017-12-15.18:14:10.450>
labels = ['3.8', '3.7', 'tests']
title = 'Dict order is now guaranteed, so add tests and doc for it'
updated_at = <Date 2018-04-04.17:36:05.903>
user = 'https://github.com/rhettinger'

    bugs.python.org fields:

    activity = <Date 2018-04-04.17:36:05.903>
actor = 'ned.deily'
assignee = 'none'
closed = True
closed_date = <Date 2018-04-04.17:36:05.905>
closer = 'ned.deily'
components = ['Tests']
creation = <Date 2017-12-15.18:14:10.450>
creator = 'rhettinger'
dependencies = []
files = []
hgrepos = []
issue_num = 32337
keywords = ['patch']
message_count = 11.0
messages = ['309060', '309114', '311490', '311585', '313624', '314916', '314917', '314918', '314920', '314930', '314943']
nosy_count = 7.0
nosy_names = ['rhettinger', 'ned.deily', 'steven.daprano', 'methane', 'xiang.zhang', 'shangdahao', 'miss-islington']
pr_nums = ['4973', '6368']
priority = None
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue32337'
versions = ['Python 3.7', 'Python 3.8']
    @rhettinger rhettinger self-assigned this Dec 15, 2017
    @rhettinger rhettinger added 3.7 (EOL) end of life tests Tests in the Lib/test dir labels Dec 15, 2017
    @rhettinger rhettinger changed the title Dict order is now guaranteed, so add tests for it Dict order is now guaranteed, so add tests and doc for it Dec 15, 2017
    @methane
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    methane commented Dec 26, 2017

    FYI, Builtin dict is tested for ordering already:

    cpython/Lib/test/test_ordered_dict.py

    Lines 646 to 662 in 13a6c09

    class CPythonBuiltinDictTests(unittest.TestCase):
    """Builtin dict preserves insertion order.
    Reuse some of tests in OrderedDict selectively.
    """
    module = builtins
    OrderedDict = dict
    for method in (
    "test_init test_update test_abc test_clear test_delitem " +
    "test_setitem test_detect_deletion_during_iteration " +
    "test_popitem test_reinsert test_override_update " +
    "test_highly_nested test_highly_nested_subclass " +
    "test_delitem_hash_collision ").split():
    setattr(CPythonBuiltinDictTests, method, getattr(OrderedDictTests, method))
    del method

    @shangdahao
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    shangdahao mannequin commented Dec 28, 2017

    Thanks inada, I removed the tests from the PR.

    @zhangyangyu
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    This part needs editing too, the text and example. https://docs.python.org/3/library/stdtypes.html#dictionary-view-objects

    @shangdahao
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    shangdahao mannequin commented Feb 4, 2018

    Thanks zhang, I have updated it in the PR.

    @rhettinger rhettinger removed their assignment Feb 4, 2018
    @ned-deily
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    Raymond, do you want to review the current state of the PR before 3.7.0b4? Otherwise, I'll probably ask that it be merged as is.

    @stevendaprano
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    I started to add this comment to bpo-33218 but Raymond closed that ticket while I was editing it.

    In 3.6, dicts preserving insertion order remains an implementation detail that cannot be relied on. It only becomes a guarantee in 3.7.

    Even in 3.7, I think that it remains best to think of dicts as fundamentally unordered. Dicts might preserve insertion order, but there's no interface for extracting the n-th item, or re-ordering the keys into some alternative order, and for the purposes of equality comparisons, the order is ignored.

    I propose changing the description from "It is best to think of a dictionary as an unordered set of key: value pairs" to something like:

    Dicts are an otherwise unordered set of key:value pairs
that remember the order keys were inserted.

    and references to "arbitrary order" should be replaced by "insertion order". But by no means should we suggest that dicts are fundamentally orderable (sortable).

    @methane
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    methane commented Apr 4, 2018

    I started to add this comment to bpo-33218 but Raymond closed that ticket while I was editing it.

    Sorry, I closed it, not Raymond.

    @methane
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    methane commented Apr 4, 2018

    New changeset dfbbbf1 by INADA Naoki (hui shang) in branch 'master':
    bpo-32337: Update documentats about dict order (GH-4973)
    dfbbbf1

    @miss-islington
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    New changeset 9216dff by Miss Islington (bot) in branch '3.7':
    bpo-32337: Update documentats about dict order (GH-4973)
    9216dff

    @methane
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    methane commented Apr 4, 2018

    Any other known issue? May I close this issue?

    @ned-deily
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    Thanks for doing this! Let's close it. If comments arise prior to its release in 370b4, we can reopen, otherwise please open a new issue.

    @ned-deily ned-deily added the 3.8 only security fixes label Apr 4, 2018
    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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