I created several instances and got ResourceWarnings as follows:
/usr/lib/python3.6/site-packages/dbus_next/introspection.py:172: ResourceWarning: unclosed <socket.socket fd=26, family=AddressFamily.AF_UNIX, type=2049, proto=0, raddr=/run/dbus/system_bus_socket>

Looking into the source code, it seems that there is no place that closes bus underlying sockets.
There is the method disconnect() that calls shutdown() but not close().
There is the method _finalize().
However I am not sure how to use these.
Close() is never called.

I am currently using the following, which is awkward and not sure if correct:
bus.disconnect()
bus._finalize()
await bus.wait_for_disconnect()
bus._sock.close()

Any idea how to correctly close sockets?