[New-bugs-announce] [issue40025] enum: _generate_next_value_ is not called if its definition occurs after calls to auto()

[Luis E.]

New submission from Luis E. <edd at asustin.net>:

I ran into this issue when attempting to add a custom _generate_next_value_ method to an existing Enum. Adding the method definition to the bottom of the class causes it to not be called at all:

from enum import Enum, auto

class E(Enum):
	A = auto()
	B = auto()
	def _generate_next_value_(name, *args):
		return name


E.B.value  # Returns 2, E._generate_next_value_ is not called

class F(Enum):
	def _generate_next_value_(name, *args):
		return name
	A = auto()
	B = auto()
	
	
F.B.value  # Returns 'B', as intended


I do not believe that the order of method/attribute definition should affect the behavior of the class, or at least it should be mentioned in the documentation.

----------
assignee: docs at python
components: Documentation, Library (Lib)
messages: 364665
nosy: docs at python, edd07
priority: normal
severity: normal
status: open
title: enum: _generate_next_value_ is not called if its definition occurs after calls to auto()
type: behavior
versions: Python 3.7

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Python tracker <report at bugs.python.org>
<https://bugs.python.org/issue40025>
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