Enum works in python 3.10 breaks in 3.11

Bug report

I have this (simplified) code

from enum import Enum, auto, unique

@unique
class TokenType(Enum):
	# // Single-character tokens.
	LEFT_PAREN = '('
	
	# // Literals.
	IDENTIFIER = auto()
	STRING = auto()
	NUMBER = auto()
	
	# // Keywords.
	AND = 'and'
	
	WHILE = 'while'

	EOF = auto()

I tested this (I developed it) using python 3.10.8.

My friend ran it in 3.11.3 and it breaks like this:

  File ".../3.11.3/lib/python3.11/enum.py", line 1561, in unique
    raise ValueError('duplicate values found in %r: %s' %
ValueError: duplicate values found in <enum 'TokenType'>: NUMBER -> STRING, EOF -> STRING

We can work around the problem using a StrEnum and it's all fine. But I think this is a regression bug. I don't think my code should break like this because the standard library changed.
Also, fyi, StrEnum is new in 3.11 so I cannot just adjust my own code (which works well).

Linked PRs

pythongh-104271: Fix auto() fallback in case of mixed type Enum

@naringas

I confirmed the issue and proposed a fix in gh-104279

I think iterating the list of last_values in gh-91457 in sorted order (instead of reversed sorted order) was an oversight

in any case, @naringas, it seems that this use of auto() will be deprecated in 3.13.
you should be able to fix this in your code by overriding _generate_next_value_ to get your desired behavior in a way that works with older python versions.

@naringas

in any case, @naringas, it seems that this use of auto() will be deprecated in 3.13. you should be able to fix this in your code by overriding _generate_next_value_ to get your desired behavior in a way that works with older python versions.

I think the issue came from how I use Enum with mixed values; I have values either as strings, or 'auto'.

Now that I've had to think about this, I realize expect unique (hence the decorator to error out if this fails) numerical values. I think this is a valid expectation for a unique Enum type with mixed values.

question: this issue gets closed if/when the PR gets merged?

@ethanfurman

@ethanfurman

question: this issue gets closed if/when the PR gets merged?

I think so, although it's up to the codeowner (Ethan) to decide if and how this should be fixed

@ethanfurman

@ethanfurman what do you think about this issue and proposed fix?

Apologies for the delay, I'll try to get to this this week. In general I agree with the proposed solution.

Merge branch '3.12' into pythongh-104271

[3.12] gh-104271: Fix auto() fallback in case of mixed type Enum (GH-…

[3.12] pythongh-104271: Fix auto() fallback in case of mixed type Enum (

[3.11] gh-104271: Fix auto() fallback in case of mixed type Enum (GH-…

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Enum works in python 3.10 breaks in 3.11 #104271

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Enum works in python 3.10 breaks in 3.11 #104271

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itamaro commented on May 7, 2023

naringas commented on May 7, 2023

sunmy2019 commented on May 8, 2023

itamaro commented on May 8, 2023

itamaro commented on May 20, 2023

ethanfurman commented on May 22, 2023

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