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bpo-40025:The behavior is the same when _generate_next_value_ is defined afte…#19904

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bpo-40025:The behavior is the same when _generate_next_value_ is defined afte…#19904
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hongweipeng:fix_enum_generate_next_value

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@hongweipeng

@hongweipeng hongweipeng commented May 4, 2020 •
edited by bedevere-bot
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…r or before members

https://bugs.python.org/issue40025

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hongweipeng requested a review from ethanfurman as a code owner May 4, 2020 16:37
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ethanfurman requested changes May 4, 2020
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I like the idea, but it needs more work. Currently, even if _generate_next_value_ is defined before any members it still will not be called until after the entire Enum is defined and given to EnumMeta.__new__ for final processing, which means that somebody wanting to do interesting things with previous member values would not be able to.

In _EnumDict you'll need to track if auto() has been seen yet, if _generate_next_value_ was defined before any uses of auto() were, and call _generate_next_value_ within _EnumDict if and only if _generate_next_value_ was defined before all uses of auto().

So this should work:

class Test1(Enum):
    def _generate_next_value(...):
        return 12
    first = auto()
    second = first + 9

and this should fail:

class Test2(Enum):
    first = auto()
    def _generate_next_value(...):
        return 12
    second = first + 9

Also, make sure you have spaces after commas, etc.

Comment thread Lib/enum.py Outdated
Comment thread Lib/enum.py Outdated
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bedevere-bot commented May 4, 2020

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A Python core developer has requested some changes be made to your pull request before we can consider merging it. If you could please address their requests along with any other requests in other reviews from core developers that would be appreciated.

Once you have made the requested changes, please leave a comment on this pull request containing the phrase I have made the requested changes; please review again. I will then notify any core developers who have left a review that you're ready for them to take another look at this pull request.

And if you don't make the requested changes, you will be put in the comfy chair!

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bedevere-bot commented May 5, 2020

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Thanks for making the requested changes!

@ethanfurman: please review the changes made to this pull request.

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bedevere-bot requested a review from ethanfurman May 5, 2020 06:01
@ethanfurman

ethanfurman commented Sep 16, 2020

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I had hoped to incorporate this idea when I had time to look at it further; unfortunately, now that I have I do not see a way to support the following use-case (which I believe would be much more common):

class I(Enum):
    first = auto()
    second = first + 2

HongWeipeng, thank you for trying.

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