New metaclass example for Data Model topic

[andresdelfino]

BPO	33816
Nosy	@rhettinger, @methane, @andresdelfino, @miss-islington
PRs	bpo-33816: Remove outdated metaclass example #7566 [3.7] bpo-33816: Remove outdated metaclass example (GH-7566) #10567 [3.6] bpo-33816: Remove outdated metaclass example (GH-7566) #10568

^{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 = None
created_at = <Date 2018-06-09.17:59:20.658>
labels = ['3.8', 'type-feature', '3.7', 'docs']
title = 'New metaclass example for Data Model topic'
updated_at = <Date 2018-11-16.11:58:12.221>
user = 'https://github.com/andresdelfino'

bugs.python.org fields:

activity = <Date 2018-11-16.11:58:12.221>
actor = 'miss-islington'
assignee = 'docs@python'
closed = False
closed_date = None
closer = None
components = ['Documentation']
creation = <Date 2018-06-09.17:59:20.658>
creator = 'adelfino'
dependencies = []
files = []
hgrepos = []
issue_num = 33816
keywords = ['patch']
message_count = 7.0
messages = ['319166', '319167', '319176', '319178', '329989', '329990', '329991']
nosy_count = 5.0
nosy_names = ['rhettinger', 'methane', 'docs@python', 'adelfino', 'miss-islington']
pr_nums = ['7566', '10567', '10568']
priority = 'normal'
resolution = None
stage = 'patch review'
status = 'open'
superseder = None
type = 'enhancement'
url = 'https://bugs.python.org/issue33816'
versions = ['Python 3.6', 'Python 3.7', 'Python 3.8']

[andresdelfino]

Since Python 3.6, when PEP-520 was accepted, class attribute definition order is preserved. That alone is sufficient to replace the example, but then 3.7 came with guaranteed dictionary insertion order. The metaclass example uses OrderedDict, what may cause confusing to new programmers, since it is not needed.

I'm creating this issue in case someone who actually has used metaclasses can come up with an example, but I'll try to find/think of an example myself.

[andresdelfino]

I'm talking about the example in Data Model, 3.3.3.6.

[rhettinger]

Probably, the entire section with the OrderedClass example should be removed. Once class dicts became ordered by default, the __prepare__ attribute lost its principal motivating use case.

[andresdelfino]

To what section are you refering by "the entire section"?

On a side note: I'll make a PR to remove the example. IMHO, there should be an example to give some idea of what a metaclass can do, but the current example is no longer useful and it's confusing because of how dicts now work.

[methane]

New changeset c2ccac7 by INADA Naoki (Andrés Delfino) in branch 'master':
bpo-33816: Remove outdated metaclass example (GH-7566)
c2ccac7

[miss-islington]

New changeset 1b80a37 by Miss Islington (bot) in branch '3.7':
bpo-33816: Remove outdated metaclass example (GH-7566)
1b80a37

[miss-islington]

New changeset 46fa7a6 by Miss Islington (bot) in branch '3.6':
bpo-33816: Remove outdated metaclass example (GH-7566)
46fa7a6

[furkanonder]

@methane Issue seems to have been resolved. Can we close the issue?