Enum._missing_ doesn't raise TypeError when a non-Enum object is a returned

[PaulPinterits]

BPO	34536
Nosy	@vstinner, @ethanfurman, @tirkarthi
PRs	bpo-34536: raise error for invalid _missing_ results #9147 bpo-34536: raise error for invalid _missing_ results #9147 bpo-34536: raise error for invalid _missing_ results #9147 [3.7] bpo-34536: raise error for invalid _missing_ results (GH-9147) #9381 [3.7] bpo-34536: raise error for invalid _missing_ results (GH-9147) #9978 bpo-34536: Cleanup test_enum imports #9979

^{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 = 'https://github.com/ethanfurman'
closed_at = <Date 2019-07-16.03:17:12.404>
created_at = <Date 2018-08-28.19:37:44.217>
labels = ['3.7', 'type-bug', 'library']
title = "Enum._missing_ doesn't raise TypeError when a non-Enum object is a returned"
updated_at = <Date 2019-07-16.03:17:12.403>
user = 'https://bugs.python.org/PaulPinterits'

bugs.python.org fields:

activity = <Date 2019-07-16.03:17:12.403>
actor = 'ethan.furman'
assignee = 'ethan.furman'
closed = True
closed_date = <Date 2019-07-16.03:17:12.404>
closer = 'ethan.furman'
components = ['Library (Lib)']
creation = <Date 2018-08-28.19:37:44.217>
creator = 'Paul Pinterits'
dependencies = []
files = []
hgrepos = []
issue_num = 34536
keywords = ['patch', 'patch', 'patch']
message_count = 7.0
messages = ['324282', '325165', '328071', '328086', '328089', '328090', '328091']
nosy_count = 4.0
nosy_names = ['vstinner', 'ethan.furman', 'Paul Pinterits', 'xtreak']
pr_nums = ['9147', '9147', '9147', '9381', '9978', '9979']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue34536'
versions = ['Python 3.7']

[PaulPinterits]

In a conversation with Ethan Furman (the author of the enum module) I've been informed that Enum automatically checks whether the _missing_ method has returned an instance of the correct class, and raises a TypeError if not. (Link: https://stackoverflow.com/a/52064774/1222951)

However, this simply does not happen.

import enum

class MyEnum(enum.Enum):
    FOO = "foo"

    @classmethod
    def _missing_(cls, value):
        return 5

print(MyEnum('bar'))  # output: 5

[ethanfurman]

New changeset 019f0a0 by Ethan Furman in branch 'master':
bpo-34536: raise error for invalid _missing_ results (GH-9147)
019f0a0

[vstinner]

I wrote PR 9978 to backport the fix to Python 3.7.

Should the fix be backported to Python 3.6 as well?

[ethanfurman]

Change by STINNER Victor:

pull_requests: +9319

Why does the above say 9319 when the PR is 9978?

[ethanfurman]

New changeset 0f2fc8b by Ethan Furman (Victor Stinner) in branch '3.7':
bpo-34536: raise error for invalid _missing_ results (GH-9147) (GH-9978)
0f2fc8b

[vstinner]

Why does the above say 9319 when the PR is 9978?

Roundup (the software running bugs.python.org) logs its own internal identifier for pull requests. Following https://bugs.python.org/pull_request9320 may help you to understand :-)

[ethanfurman]

New changeset 4acf6c9 by Ethan Furman (Victor Stinner) in branch 'master':
bpo-34536: Cleanup test_enum imports (GH-9979)
4acf6c9