I use CoC.vim [0] with whatever Python plugin they recommend and it's easily been the most painless autocompletion I've ever used in over a decade of Vim. I wrote some (admittedly pretty basic) Python with it last week with no complaints!
The python plugin that is recommended has switched from `pyls` to the Microsoft Python
Language Server (the same one that powers the Visual Studio Code Python extension),
written in C#. The extension comes bundled with a .NET Core interpreter.