I have a Python script without any build scripts on AUR too. If you want have a look, it simply copies (with install command) to /usr/bin. In my case its a commandline application, so there is no need for a desktop file. But for a GUI tool I would add a desktop file too.
I’m trying to port the Mynah XMPP client.
I don't think creating an installer script can be called a "port", unless you are making changes to adapt to a specific environment. I would clarify this in the post description, as this is not really a port, but just creating an installer. Otherwise one might get confused.