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Unreachable condition: if enum_class._member_type_ is object #90454

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sobolevn opened this issue Jan 7, 2022 · 5 comments
Closed

Unreachable condition: if enum_class._member_type_ is object #90454

sobolevn opened this issue Jan 7, 2022 · 5 comments
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@ethanfurman
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3.11 only security fixes tests Tests in the Lib/test dir

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@sobolevn
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sobolevn commented Jan 7, 2022

BPO 46296
Nosy @ethanfurman, @sobolevn
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  • bpo-46296: add a test case for enum.py which covers _use_args == True and _member_type_ == object #30458
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    GitHub fields:

    assignee = 'https://github.com/ethanfurman'
closed_at = <Date 2022-01-07.21:45:40.560>
created_at = <Date 2022-01-07.17:36:29.337>
labels = ['tests', '3.11']
title = 'Unreachable condition: `if enum_class._member_type_ is object`'
updated_at = <Date 2022-01-07.21:45:40.560>
user = 'https://github.com/sobolevn'

    bugs.python.org fields:

    activity = <Date 2022-01-07.21:45:40.560>
actor = 'ethan.furman'
assignee = 'ethan.furman'
closed = True
closed_date = <Date 2022-01-07.21:45:40.560>
closer = 'ethan.furman'
components = ['Tests']
creation = <Date 2022-01-07.17:36:29.337>
creator = 'sobolevn'
dependencies = []
files = []
hgrepos = []
issue_num = 46296
keywords = ['patch']
message_count = 5.0
messages = ['409989', '410026', '410033', '410040', '410041']
nosy_count = 2.0
nosy_names = ['ethan.furman', 'sobolevn']
pr_nums = ['30458']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = None
url = 'https://bugs.python.org/issue46296'
versions = ['Python 3.11']
    @sobolevn
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    sobolevn commented Jan 7, 2022

    This condition can never be True:

    cpython/Lib/enum.py

    Lines 222 to 223 in b127e70

    if enum_class._member_type_ is object:
    enum_member._value_ = value

    Why? Because:

    1. It is executed only when `if not enum_class._use_args_:`:

      cpython/Lib/enum.py

      Line 215 in b127e70

      if not enum_class._use_args_:
    2. But, `enum_class._use_args_` will always be `False` for cases when `enum_class._member_type_` is `object`
    3. It is defined here:

      cpython/Lib/enum.py

      Line 937 in b127e70

      if first_enum is None or __new__ in (Enum.__new__, object.__new__):

    So, I guess that removing this condition can simplify the enum.py.
    Coverage shows that this part is not tested.

    I will send a PR shortly.

    @sobolevn sobolevn added stdlib Python modules in the Lib dir 3.11 only security fixes labels Jan 7, 2022
    @ethanfurman
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    (2) is false.

    >>> from enum import Enum
>>> 
>>> class MyEnum(Enum):
...     def __new__(cls, value):
...         member = object.__new__(cls)
...         return member
...     ONE = 1
... 

>>> MyEnum.ONE
MyEnum.ONE

>>> MyEnum._use_args_
True

>>> MyEnum._member_type_
<class 'object'>

    If coverage shows a branch not being tested, design a test for it instead of removing the branch.

    @sobolevn
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    sobolevn commented Jan 7, 2022

    Yes, this is just a missing test. Not a wrong condition!

    @sobolevn sobolevn added tests Tests in the Lib/test dir and removed stdlib Python modules in the Lib dir labels Jan 7, 2022
    @ethanfurman
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    New changeset 74d1663 by Nikita Sobolev in branch 'main':
    bpo-46296: [Enum] add a test for missing value recovery (GH-30458)
    74d1663

    @ethanfurman
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    Thank you, Nikita!

    @ezio-melotti ezio-melotti transferred this issue from another repository Apr 10, 2022
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