style(core): fix mypy no-any-return violations by cbornet · Pull Request #34204 · langchain-ai/langchain

Christophe Bornet (cbornet) · 2025-12-04T14:34:37Z

FIxed where possible
Used cast when not possible to fix

Christophe Bornet (cbornet) · 2025-12-04T14:38:08Z

libs/core/langchain_core/language_models/chat_models.py

        # Check if a runtime streaming flag has been passed in.
        if "stream" in kwargs:
-            return kwargs["stream"]
+            return bool(kwargs["stream"])


calling bool() here doesn't change the behavior as _should_stream is always called in a if condition.

Christophe Bornet (cbornet) · 2025-12-04T14:39:05Z

libs/core/langchain_core/messages/utils.py


+_SingleMessage = BaseMessage | str | dict[str, Any]
+_T = TypeVar("_T", bound=_SingleMessage)
+# A sequence of _SingleMessage that is NOT a bare str


This is needed because otherwise str matches Sequence[str]

codspeed-hq · 2025-12-04T14:39:49Z

CodSpeed Performance Report

Merging #34204 will not alter performance

_{Comparing cbornet:core-no-return-any (370ed3f) with master (78b2d51)}

⚠️

Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

Summary

✅ 13 untouched
⏩ 21 skipped¹

21 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

Christophe Bornet (cbornet) · 2025-12-04T18:02:19Z

libs/core/langchain_core/messages/base.py


        prompt = ChatPromptTemplate(messages=[self])
-        return prompt + other
+        return prompt.__add__(other)


mypy doesn't figure the + operator...

Christophe Bornet (cbornet) · 2025-12-04T18:05:21Z

libs/core/langchain_core/runnables/base.py

                try:
                    while True:
-                        chunk = await coro_with_context(py_anext(iterator), context)
+                        chunk = await coro_with_context(anext(iterator), context)


we now use python 3.10+ so py_anext is not needed anymore

Mason Daugherty (mdrxy) · 2025-12-22T06:17:58Z

libs/core/langchain_core/runnables/utils.py

    Args:
        coro: The coroutine to await.
        context: The context to use.
-        create_task: Whether to create a task.


Removing create_task is technically breaking (even though it wasn't exposed in __init__.py)

Let's add a deprecation warning if create_task=True is passed.

Mason Daugherty (mdrxy) · 2025-12-22T06:21:56Z

libs/core/langchain_core/utils/env.py



 def get_from_dict_or_env(
-    data: dict[str, Any],


I think values is dict[str, Any] that can contain floats, objects, etc., not dict[str, str].

From its signature get_from_dict_or_env must return str and we return the value of the data dict.
So data should be dict[str, str] or else get_from_dict_or_env should be changed to return Any.

Changing to dict[str, str] would be a breaking change. I understand the type inconsistency concern. If we want stricter correctness, we could add a runtime check, but I'd lean toward keeping dict[str, Any] for compatibility for now.

I changed to call str(data[key]) so the signature doesn't break. Can you take a look again ?

Mason Daugherty (mdrxy) · 2025-12-22T06:24:40Z

libs/core/langchain_core/utils/json.py


 def _parse_json(
-    json_str: str, *, parser: Callable[[str], Any] = parse_partial_json
+    json_str: str, *, parser: Callable[[str], dict[str, Any]] = parse_partial_json


parse_partial_json is typed to return Any, not dict[str, Any]

Yes but mypy misses it and doesn't complain, so there's no need to cast.

The other possibility would be to make _parse_json/parse_json_markdown return Any which would be closer to the truth. And have callers cast or check the type the result. There are callers of parse_json_markdown in core, langchain-classic and community.
It seems some callers already expect parse_json_markdown to return something different than a dict and have isinstance checks (eg. JSONAgentOutputParser.parse)
LMK what you prefer.

Mypy not catching something doesn't make the types correct. I think making both return Any is a more honest approach.

Mason Daugherty (mdrxy) · 2025-12-22T06:47:44Z

^outside of the above, looks good!

Copilot

Pull request overview

This PR addresses mypy's no-any-return violations by fixing type annotations and adding explicit casts where necessary. The main goal is to enable stricter mypy checking by removing the warn_return_any = false configuration setting.

Key Changes:

Added explicit type parameters to generic classes (e.g., RunnableLambda[int, int])
Added cast statements to satisfy mypy where type inference fails
Fixed return types and improved type annotations throughout the codebase

Reviewed changes

Copilot reviewed 41 out of 41 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
libs/core/pyproject.toml	Removed `warn_return_any = false` to enable stricter type checking
libs/core/tests/unit_tests/test_tools.py	Fixed test functions to return properly typed values and convert integers to strings
libs/core/tests/unit_tests/runnables/test_utils.py	Added type parameters to `RunnableLambda` instances and fixed return type casting
libs/core/tests/unit_tests/runnables/test_tracing_interops.py	Added type parameters to `RunnableLambda` and added explicit casting for dictionary access
libs/core/tests/unit_tests/runnables/test_runnable_events_v2.py	Added type parameters to `RunnableLambda` instances
libs/core/tests/unit_tests/runnables/test_runnable_events_v1.py	Added type parameters to `RunnableLambda` instances
libs/core/tests/unit_tests/runnables/test_runnable.py	Added explicit integer casting for kwargs values
libs/core/tests/unit_tests/runnables/test_history.py	Fixed assertion statement that was incorrectly chained and updated type hint
libs/core/tests/unit_tests/pydantic_utils.py	Replaced `is_basemodel_subclass` with direct `issubclass` checks
libs/core/tests/unit_tests/prompts/test_structured.py	Replaced `is_basemodel_subclass` with direct `issubclass` check
libs/core/tests/unit_tests/messages/test_utils.py	Reorganized type ignore comment placement
libs/core/langchain_core/vectorstores/utils.py	Added cast for numpy array return value
libs/core/langchain_core/utils/*.py	Added casts and improved type annotations across utility modules
libs/core/langchain_core/tracers/*.py	Added casts for dictionary access and improved return type annotations
libs/core/langchain_core/tools/*.py	Added casts for Pydantic model creation and schema access
libs/core/langchain_core/runnables/*.py	Added type parameters and improved type annotations
libs/core/langchain_core/prompts/*.py	Added casts, improved type annotations, and added abstract method declaration
libs/core/langchain_core/output_parsers/*.py	Added overloads and improved return type handling
libs/core/langchain_core/messages/*.py	Enhanced type checking with runtime validation and added casts
libs/core/langchain_core/language_models/*.py	Added casts for serialization and improved type annotations
libs/core/langchain_core/_api/internal.py	Added cast for module name access

Comments suppressed due to low confidence (1)

libs/core/tests/unit_tests/runnables/test_history.py:1

The assertion on line 100 is now separate from the list comprehension on line 98, but output will be a list containing the boolean result of the comparison that was previously on line 99. The code should assign the result of the list comprehension to output before asserting. Remove the comparison from inside the list comprehension and keep it only in the assert statement.

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Copilot · 2025-12-26T04:14:26Z

libs/core/langchain_core/prompts/string.py

        return StringPromptValue(text=await self.aformat(**kwargs))

+    @override
+    @abstractmethod


Adding an abstract method declaration to a base class that likely already has concrete implementations in subclasses could break existing code. If format is already implemented in this class elsewhere (not visible in the diff), this abstract declaration is incorrect. Verify that this method is not already implemented in StringPromptTemplate or ensure all subclasses properly override it.

Suggested change

@abstractmethod

Hi Copilot, you missed that this is an override of the parent method which is already abstract so it doesn't break anything 😉.

Mason Daugherty (mdrxy)

TY!

* FIxed where possible * Used `cast` when not possible to fix --------- Co-authored-by: Mason Daugherty <github@mdrxy.com> Co-authored-by: Mason Daugherty <mason@langchain.dev>

Christophe Bornet (cbornet) requested a review from Eugene Yurtsev (eyurtsev) as a code owner December 4, 2025 14:34

github-actions bot added infra PRs made that include chores, devops, repo meta changes core `langchain-core` package issues & PRs and removed infra PRs made that include chores, devops, repo meta changes labels Dec 4, 2025

Christophe Bornet (cbornet) force-pushed the core-no-return-any branch from dcb7159 to 3a71eb2 Compare December 4, 2025 14:36

Christophe Bornet (cbornet) commented Dec 4, 2025

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Christophe Bornet (cbornet) force-pushed the core-no-return-any branch 2 times, most recently from cce7d38 to ca9ecff Compare December 4, 2025 17:26

github-actions bot added the dependencies Pull requests that update a dependency file (e.g. `pyproject.toml` or `uv.lock`) label Dec 4, 2025

Christophe Bornet (cbornet) changed the title ~~chore(core): fix some no-return-any mypy violations~~ chore(core): fix mypy no-any-return rules Dec 4, 2025

github-actions bot added the infra PRs made that include chores, devops, repo meta changes label Dec 4, 2025

Christophe Bornet (cbornet) changed the title ~~chore(core): fix mypy no-any-return rules~~ chore(core): fix mypy no-any-return violations Dec 4, 2025

github-actions bot added infra PRs made that include chores, devops, repo meta changes and removed infra PRs made that include chores, devops, repo meta changes labels Dec 4, 2025

Christophe Bornet (cbornet) commented Dec 4, 2025

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Christophe Bornet (cbornet) force-pushed the core-no-return-any branch 2 times, most recently from 31cf767 to 1bac6c8 Compare December 9, 2025 16:56

Mason Daugherty (mdrxy) changed the title ~~chore(core): fix mypy no-any-return violations~~ style(core): fix mypy no-any-return violations Dec 20, 2025

github-actions bot added linting and removed infra PRs made that include chores, devops, repo meta changes labels Dec 20, 2025

Mason Daugherty (mdrxy) reviewed Dec 22, 2025

View reviewed changes

chore(core): fix RunnablePick method return types

6f65bfd

Christophe Bornet (cbornet) and others added 4 commits December 22, 2025 10:10

cast remaining return types

58ae69a

fix

ae22c7f

cr

3c9256b

cr

3b5be0f

Christophe Bornet (cbornet) force-pushed the core-no-return-any branch 2 times, most recently from 6957e92 to 597ad79 Compare December 22, 2025 10:35

Changes following review

8826c21

Christophe Bornet (cbornet) force-pushed the core-no-return-any branch from 597ad79 to 8826c21 Compare December 22, 2025 11:14

Mason Daugherty (mdrxy) requested a review from Copilot December 26, 2025 04:10

Copilot AI reviewed Dec 26, 2025

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Changes following review

5d5e90f

Christophe Bornet (cbornet) force-pushed the core-no-return-any branch from 456c0fb to 5d5e90f Compare December 26, 2025 10:10

github-actions bot added the langchain-classic `langchain-classic` package issues & PRs label Dec 26, 2025

Mason Daugherty (mdrxy) approved these changes Dec 27, 2025

View reviewed changes

Merge branch 'master' into core-no-return-any

370ed3f

Mason Daugherty (mdrxy) merged commit a92c032 into langchain-ai:master Dec 27, 2025
89 checks passed

Christophe Bornet (cbornet) deleted the core-no-return-any branch December 27, 2025 09:10

Mason Daugherty (mdrxy) added the external label Jan 22, 2026

Rakesh Gupta (caravin) mentioned this pull request Feb 17, 2026

get_from_dict_or_env from langchain_core.utils has incorrect signature or incorrectly casting output #35285

Open

29 tasks

Mason Daugherty (mdrxy) mentioned this pull request Feb 21, 2026

fix(core): remove str coercion in get_from_dict_or_env #35378

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Merging #34204 will not alter performance

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Mason Daugherty (mdrxy) commented Dec 22, 2025

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