When entering functions into a worksheet you will see that Excel will give you some help to complete some of it’s built in functions, and will tell you what arguments are expected.
You can get the same auto-completion behaviour for functions written with PyXLL too.
PyXLL integrates with the Excel-DNA IntelliSense add-in.
Download this add-in from https://github.com/Excel-DNA/IntelliSense/releases. Expand the "Assets" tab to see the downloads:
Once you install it into Excel, PyXLL will detect it automatically and start using it to give you auto-completion and in-sheet IntelliSense for your PyXLL functions.
If you need help installing the Excel-DNA IntelliSense add-in then the following video will help https://www.youtube.com/watch?v=-BIOzl1igXU.