ipaddress: IPv6Address integer addition discards scope ID

[augusto-rehfeldt]

Bug report

Bug description:

Documented behaviour: Python ipaddress documentation, “Arithmetic operators”: “Addition and subtraction of integers with address objects are supported.” The “Comparison operators” section also states: “Same IPv6 addresses with different scope zone IDs are not equal.” Together these make scope significant to the additive identity invariant.

Expected: IPv6Address('fe80::1%eth0'), equal to the original address.

Actual: IPv6Address('fe80::1'), unequal to the original because its scope ID is lost.

import ipaddress

s = 'fe80::1%eth0'
try:
    a = ipaddress.IPv6Address(s)
    if not a.scope_id or '%' in a.scope_id:
        print('REFUTATION REJECTED: invalid or empty scope ID')
    else:
        expected = ipaddress.IPv6Address(s)  # Identity preserves the full address.
        actual = a + 0
        if actual != expected:
            print('REFUTATION CONFIRMED:', repr(s), 'actual =', repr(actual),
                  'expected =', repr(expected))
        else:
            print('REFUTATION REJECTED: additive identity holds')
except Exception as e:
    print('REFUTATION REJECTED:', type(e).__name__, str(e))

Output on Python 3.14.6 (Windows-11-10.0.26220-SP0), standard library ipaddress:

REFUTATION CONFIRMED: 'fe80::1%eth0' actual = IPv6Address('fe80::1') expected = IPv6Address('fe80::1%eth0')

This report was found and written by an automated property-testing tool I run (bugforge). The reproducer above was executed and its output is pasted unedited; no person reviewed the report before it was filed. The search script is in https://github.com/augusto-rehfeldt/bugforge-results/tree/main/ipaddress-20261003-125643-c1

CPython versions tested on:

3.14

Operating systems tested on:

Windows

[ZeroIntensity]

Please stop or we'll have to block you.

[ZeroIntensity]

See #158748 (comment).