Bug report

When getfqdn called with name "::", instead of returning gethostname(), it will call gethostbyaddr("::").
This will raise an exception "socket.herror: [Errno 1] Unknown host", which will cause a 30 seconds(timeout) delay and return incorrect result. (Tested only on macOS Ventura 13.0.0.1, Python 3.10.6)
The solution is to add a filter to the first if statement, in line 792 socket.py, which will be included in my further pull-request.

import socket
socket.getfqdn("::") # This will block 30 seconds and returns "::" instead of hostname

Your environment

• CPython versions tested on: Python 3.10.6 (main, Aug 11 2022, 13:36:31) [Clang 13.1.6 (clang-1316.0.21.2.5)] on Darwin
• Operating system and architecture: macOS Ventura 13.0.0.1, arm64

Linked PRs

• gh-100374: Fixed a bug in socket.getfqdn() #100375
• [3.11] gh-100374: Fixed a bug in socket.getfqdn() (gh-100375) #100401
• [3.10] gh-100374: Fixed a bug in socket.getfqdn() (gh-100375) #100402