Minor enhancement of the LangChain integration docs

Path: /integrations/langchain

This is a suggestion for a minor improvement of the LangChain integration docs.

Environment

Python v3.11.6
chainlit v0.7.603
MacOS Sonoma v14.0
VS Code Pylance extension v2023.11.10, powered by the static type checker Pyright

Problem

The below code, generates an inconvenient warning from Pylance in VS Code.

Code:

runnable = cl.user_session.get("runnable")  # type: Runnable

Warning:

Expression of type "Unknown | None" cannot be assigned to declared type "Runnable[Unknown, Unknown]" Type "Unknown | None" cannot be assigned to type "Runnable[Unknown, Unknown]" Type "None" cannot be assigned to type "Runnable[Unknown, Unknown]" Pylance(reportGeneralTypeIssues)

Pylance suggests that the code cannot guarantee that the .get("runnable") call returns a Runnable.

This is an inconvenience when copy-pasting to get started with chainlit.

Solution

I suggest you change the docs to the following, to inform the type checker that we will always receive a value with the type Runnable:

from typing import cast

# (..)

runnable = cast(Runnable, cl.user_session.get("runnable"))

# (...)

Would make a PR directly, but the repo seems to require me to create a fork, so I'm taking the lazy route and just raising an issue ;-)

Potential Limitations

typing.cast was introduced in Python 3.5 together with the typing module, so if you only support Python v3.5+, this change should work for everyone. If it's correct that chainlit currently supports >=3.8.1 and <3.12, the change should be fine.
Have not tested this with any other type checker.

Chainlit / docs