pygls: The Generic Language Server Framework

pygls (pronounced like "pie glass") is a pythonic generic implementation of the Language Server Protocol for use as a foundation for writing your own Language Servers in just a few lines of code.

Quickstart

from pygls.server import LanguageServer
from lsprotocol.types import (
    TEXT_DOCUMENT_COMPLETION,
    CompletionItem,
    CompletionList,
    CompletionParams,
)

server = LanguageServer("example-server", "v0.1")

@server.feature(TEXT_DOCUMENT_COMPLETION)
def completions(params: CompletionParams):
    items = []
    document = server.workspace.get_document(params.text_document.uri)
    current_line = document.lines[params.position.line].strip()
    if current_line.endswith("hello."):
        items = [
            CompletionItem(label="world"),
            CompletionItem(label="friend"),
        ]
    return CompletionList(is_incomplete=False, items=items)

server.start_io()

Which might look something like this when you trigger autocompletion in your editor:

Docs and Tutorial

The full documentation and a tutorial are available at https://pygls.readthedocs.io/en/latest/.

Projects based on pygls

We keep a table of all known pygls implementations. Please submit a Pull Request with your own or any that you find are missing.

Alternatives

The main alternative to pygls is Microsoft's NodeJS-based Generic Language Server Framework. Being from Microsoft it is focussed on extending VSCode, although in theory it could be used to support any editor. So this is where pygls might be a better choice if you want to support more editors, as pygls is not focussed around VSCode.

There are also other Language Servers with "general" in their descriptons, or at least intentions. They are however only general in the sense of having powerful configuration. They achieve generality in so much as configuration is able to, as opposed to what programming (in pygls' case) can achieve.