Thanks, @movq! That seems to be much easier. It's already implemented in the Python docs as examples of recvmsg(…) and sendmsg(…):

• https://docs.python.org/3/library/socket.html#socket.socket.recvmsg
• https://docs.python.org/3/library/socket.html#socket.socket.sendmsg

I looked at them sooo many times in order to figure out why my SCM_CREDENTIALS sending code didn't work. :-D