62f255980d
Enables mypy's `warn_unreachable` rule for `langchain-core`, bringing it
in line with the other strict libraries in the monorepo. Previously this
rule was intentionally disabled by a code comment, because under mypy
2.x it false-flags intentional defensive runtime checks — most notably
the SSRF / IP-policy guards in `langchain_core/_security/` — as
unreachable.
This PR resolves all of those warnings without deleting or
blanket-ignoring the defensive guards, so contributors get
unreachable-code coverage going forward and accidental dead code is
caught in CI.
The bulk of the change is mechanical: a targeted `# type:
ignore[unreachable]` on each defensive `else`/error branch that mypy
considers unreachable but that we deliberately keep as a runtime guard
against unexpected input. A few changes are more substantive and worth a
closer look:
- **`coro_with_context` (`runnables/utils.py`) — behavior change on
Python < 3.11.** The pre-3.11 path is rewritten to always route through
`context.run(asyncio.create_task, coro)`, so the supplied context is
reliably propagated to the task. Previously, on 3.10 the helper returned
the bare coroutine (run in the caller's context) when
`create_task=False`, and dropped the context entirely when
`create_task=True`. The new behavior matches 3.11+. The `create_task`
parameter is now inert but retained for signature compatibility. All
callers `await` the result, so returning a `Task` rather than a
coroutine is transparent.
- **`_create_template_from_message_type` (`prompts/chat.py`) — signature
widening.** This private helper's `template` parameter now accepts
`bool` inside the list, accurately reflecting the existing `["{var}",
is_optional]` placeholder form. No public-API impact.
- **`PydanticOutputFunctionsParser`
(`output_parsers/openai_functions.py`).** The `pydantic_schema` field is
typed as `TypeBaseModel` (which covers both v1 and v2 model classes,
unlike the prior annotation), and the `args_only` parse path now
dispatches explicitly on `BaseModel` vs `BaseModelV1` rather than
duck-typing via `hasattr`. This also yields clearer errors for
unsupported / dict schemas.
- **`_security/_policy.py`.** Loop variables are renamed so mypy can
narrow their types, which lets the old `# type: ignore[assignment]`
comments be dropped. The IP-blocklist logic is unchanged.
---------
Co-authored-by: Mason Daugherty <mason@langchain.dev>
Co-authored-by: Mason Daugherty <github@mdrxy.com>
🦜🍎️ LangChain Core
Looking for the JS/TS version? Check out LangChain.js.
To help you ship LangChain apps to production faster, check out LangSmith. LangSmith is a unified developer platform for building, testing, and monitoring LLM applications.
Quick Install
uv add langchain-core
🤔 What is this?
LangChain Core contains the base abstractions that power the LangChain ecosystem.
These abstractions are designed to be as modular and simple as possible.
The benefit of having these abstractions is that any provider can implement the required interface and then easily be used in the rest of the LangChain ecosystem.
⛰️ Why build on top of LangChain Core?
The LangChain ecosystem is built on top of langchain-core. Some of the benefits:
- Modularity: We've designed Core around abstractions that are independent of each other, and not tied to any specific model provider.
- Stability: We are committed to a stable versioning scheme, and will communicate any breaking changes with advance notice and version bumps.
- Battle-tested: Core components have the largest install base in the LLM ecosystem, and are used in production by many companies.
📖 Documentation
For full documentation, see the API reference. For conceptual guides, tutorials, and examples on using LangChain, see the LangChain Docs. You can also chat with the docs using Chat LangChain.
📕 Releases & Versioning
See our Releases and Versioning policies.
💁 Contributing
As an open-source project in a rapidly developing field, we are extremely open to contributions, whether it be in the form of a new feature, improved infrastructure, or better documentation.
For detailed information on how to contribute, see the Contributing Guide.
Resources
- LangChain Academy — comprehensive, free courses on LangChain libraries and products, made by the LangChain team
- Code of Conduct — community guidelines and standards