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vars() manipulation encounters problems with Enum #75982

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ethanfurman opened this issue Oct 17, 2017 · 3 comments
Closed

vars() manipulation encounters problems with Enum #75982

ethanfurman opened this issue Oct 17, 2017 · 3 comments
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@ethanfurman
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3.7 (EOL) end of life type-bug An unexpected behavior, bug, or error

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@ethanfurman
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BPO 31801
Nosy @warsaw, @ethanfurman, @eric-wieser
PRs
  • bpo-31801: Enum: add _ignore_ as class option #5237
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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 = 'https://github.com/ethanfurman'
closed_at = <Date 2018-09-10.18:30:27.608>
created_at = <Date 2017-10-17.00:21:55.188>
labels = ['type-bug', '3.7']
title = 'vars() manipulation encounters problems with Enum'
updated_at = <Date 2018-09-10.18:30:27.607>
user = 'https://github.com/ethanfurman'

    bugs.python.org fields:

    activity = <Date 2018-09-10.18:30:27.607>
actor = 'ethan.furman'
assignee = 'ethan.furman'
closed = True
closed_date = <Date 2018-09-10.18:30:27.608>
closer = 'ethan.furman'
components = []
creation = <Date 2017-10-17.00:21:55.188>
creator = 'ethan.furman'
dependencies = []
files = []
hgrepos = []
issue_num = 31801
keywords = ['patch']
message_count = 3.0
messages = ['304487', '306257', '310425']
nosy_count = 4.0
nosy_names = ['barry', 'eli.bendersky', 'ethan.furman', 'Eric.Wieser']
pr_nums = ['5237']
priority = 'normal'
resolution = 'fixed'
stage = 'resolved'
status = 'closed'
superseder = None
type = 'behavior'
url = 'https://bugs.python.org/issue31801'
versions = ['Python 3.7']
    @ethanfurman
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    The following code should work (from https://stackoverflow.com/a/46780742/208880):

        class BaudRate(Enum):

        cls = vars()
        regexp = r"(?:^|,)B(?P<rate>\d+)"
        rates = sorted(map(int, re.findall(regexp, ",".join(dir(termios)))))
        for value in rates:
            cls['B%d' % value] = value

        @classmethod
        def valid_rate(cls, value):
            return (any(value == item.value for item in cls))

    This doesn't work because EnumMeta does not allow names to be reassigned nor deleted. aenum gets around this by allowing an _ignore_ attribute which contains the names that should not be tracked (and, in fact, those names are removed from the final class).

    Unless a better idea is put forward, I will add _ignore_ support to Enum.

    @ethanfurman ethanfurman added the 3.7 (EOL) end of life label Oct 17, 2017
    @ethanfurman ethanfurman self-assigned this Oct 17, 2017
    @ethanfurman ethanfurman added the type-bug An unexpected behavior, bug, or error label Oct 17, 2017
    @eric-wieser
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    eric-wieser mannequin commented Nov 15, 2017

    Not necessarily an argument against this feature, but two workarounds exist for this already:

    1. Use nonlocal to prevent value going into the class namespace:
        value = None
    
    class BaudRate(enum.Enum):    
        nonlocal value
        for value in rates:
            locals()['B%d' % value] = value
    
        @classmethod
        def valid_rate(cls, value):
            return (any(value == item.value for item in cls))
    1. Use types.new_class, which is more suited to dynamic class creation anyway:
        def make_cls(ns):
        for value in rates:
            ns['B%d' % value] = value

        @classmethod
        def valid_rate(cls, value):
            return (any(value == item.value for item in cls))
        ns['valid_rate'] = valid_rate

types.new_class('BaudRate', (enum.Enum,), exec_body=make_cls)

    @ethanfurman
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    New changeset a4b1bb4 by Ethan Furman in branch 'master':
    bpo-31801: Enum: add _ignore_ as class option (bpo-5237)
    a4b1bb4

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

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