ipaddress: IPv6Network.is_global violates documented endpoint classification rule

[augusto-rehfeldt]

Bug report

Bug description:

Documented behaviour: Python ipaddress documentation, IPv4Network/IPv6Network classification attributes: "These attributes are true for the network as a whole if they are true for both the network address and the broadcast address." This includes is_global.

Expected: IPv6Network('::/0').is_global is False, matching the conjunction of its endpoints' is_global values.

Actual: IPv6Network('::/0').is_global is True.

import ipaddress

s = "::/0"
try:
    n = ipaddress.IPv6Network(s, strict=True)
except ValueError as e:
    print("REFUTATION REJECTED:", e)
else:
    actual = n.is_global
    expected = n.network_address.is_global and n.broadcast_address.is_global
    if actual != expected:
        print(f"REFUTATION CONFIRMED: {s!r} actual={actual} expected={expected}")
    else:
        print("REFUTATION REJECTED: result matches documented endpoint rule")

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

REFUTATION CONFIRMED: '::/0' actual=True expected=False

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-20261003-190337-c3

CPython versions tested on:

3.14

Operating systems tested on:

Windows

[ZeroIntensity]

See #158748 (comment).