Turning on the language server

In your settings.json, set "python.languageServer": "Microsoft". You will then be prompted to restart VS Code. If you have not downloaded the language server before then that will be triggered when you trigger the extension by opening a Python file.

Issues directly related to the language server -- e.g. completions -- should be reported to the Microsoft/python-language-server issue tracker.

Checking whether you have the latest stable version

You can check what version of the language server you are using by looking at the Output Panel's Python output:

The languageServerVersion in our package.json always specifies the latest stable release version.

Installing the latest stable version

1. Run the Extensions: Open Extensions Folder command
   
2. Quit VS Code
3. Open the folder containing the Python extension (name should have a prefix of ms-python.python)
   
4. Delete the folder containing the language server (has a prefix of languageServer)
   
5. Launch VS Code
6. Open a Python file
7. Wait for the language server to download and be unpacked
   

You can check the Output panel to double-check you are using the latest version (see above for a screenshot of what the panel looks like).

Installing the beta version

If you want to try out what is coming, you can try the beta version of the language server by setting "python.analysis.downloadChannel": "beta" (note that the setting isn't documented, so don't be alarmed if VS Code flags it as not existing). Do note that this will not re-download the language server immediately, so if you want to update immediately you will need to follow the instructions above on how to delete your current installation of the language server.

As with anything that is beta, no guarantees of stability or quality can be made. If issues are found then please report them on the Microsoft/python-language-server issue tracker.