[Enum] verify'ing a Flag class with negative values results in MemoryError

[udhayprakash]

Bug report

A clear and concise description of what the bug is.
Include a minimal, reproducible example (https://stackoverflow.com/help/minimal-reproducible-example), if possible.

Your environment

from enum import Flag, verify, NAMED_FLAGS

@verify(NAMED_FLAGS)
class Color(Flag):
    RED = -1 # 0
    GREEN = 2
    BLUE = 4
    WHITE = 9 
    NEON = 6

In this example, it is working good, if RED has value of 0, but is resulting in Memory Error, if its value is changed to -1

• CPython versions tested on: 3.11.0
• Operating system and architecture: Windows 10, 64 bit

• PR: gh-99248: [Enum] fix negative number infinite loop #99256

• PR: [3.11] gh-99248: [Enum] fix negative number infinite loop (GH-99256) #99259

[JelleZijlstra]

The problem is that enum._iter_bits_lsb (

cpython/Lib/enum.py

Line 116 in c43714f

def _iter_bits_lsb(num):

) doesn't terminate for negative numbers, the number just grows unbounded.

Negative numbers don't really make sense as OR-able flags (which are conceptually unsigned), but we should fail with an obvious error instead of using all available memory.

cc @ethanfurman for enums

[ethanfurman]

Thanks for the report. Fix merged into main and 3.11.