Intellisense-like popup-help. That is. hover over a function, class, etc. and get a short description
Most Python IDEs have some sort of pop-up help. e.g. hover over a function (built-in, library, user defined) and get a pop-up showing the signature.
Also highlight (e.g. with red squiggles) errors in syntax. Highlight in blue squiggles using a variable before definition, etc.