Good point. The address info depends on the address family, https://docs.python.org/3/library/socket.html#socket-families . I have updated the doc string:

>>> import socket
>>> print(socket.socket.getsockname.__doc__)
getsockname() -> address info

Return the address of the local endpoint. The format depends on the
address family. For IPv4 sockets, the address info is a pair
(hostaddr, port).