Zero-valued flag enum has no name

[apple1417]

Documentation

Quoting Doc/howto/enum.rst:1148:

- names of pseudo-flags are constructed from their members' names::

    >>> (Color.RED | Color.GREEN).name
    'RED|GREEN'

This section was originally added in 7aaeb2a3.

If you have a zero-valued flag, and you didn't explicitly give it a name, this doesn't seem to apply, it returns None instead.

class NoZero(Flag):
    ONE = 1

class HasZero(Flag):
    ZERO = 0
    ONE = 1

print(NoZero(0).name, type(NoZero(0).name))   # None <class 'NoneType'>
print(HasZero(0).name, type(HasZero(0).name)) # ZERO <class 'str'>

I'm not entirely sure if this should be considered a documentation issue or a bug report (or both). It doesn't really feel like zero should be treated any differently from other unnamed combinations. But at the same time, I've tested, and this is already the existing behavior in 3.10 through 3.12, and it doesn't seem to be documented anywhere.

Linked PRs

• gh-118820: Zero-valued flag enum has no name #118848
• [3.12] gh-118820: Zero-valued flag enum has no name (GH-118848) #120758
• [3.13] gh-118820: Zero-valued flag enum has no name (GH-118848) #120759

[nineteendo]

The code for reference:

cpython/Lib/enum.py

Line 1507 in 82acc5f

if member_value or aliases:

cpython/Lib/enum.py

Lines 1527 to 1528 in 82acc5f

	else:
	pseudo_member._name_ = None

Added in the same commit.

[nineteendo]

cc @ethanfurman.

[ethanfurman]

The zero-flag name is constructed from its members -- it just doesn't have any members. This could certainly be mentioned in the docs.

[nineteendo]

I'll make a pull request with an example.

[nineteendo]

It has been a month, does someone still need to review my pull request?