[rusih100]

What does this PR do?

Adds an opt-in named_inputs flag to @observe. When enabled, input is recorded
by parameter name instead of {"args": [...], "kwargs": {...}}.

@observe(named_inputs=True)
def answer(query: str, lang: str): ...

answer("how do I return an item?", "en")
# Before: {"args": ["how do I return an item?", "en"], "kwargs": {}}
# After:  {"query": "how do I return an item?", "lang": "en"}

answer_before uses the default, answer_after uses named_inputs=True:

Script used for the screenshot

from langfuse import get_client, observe


@observe(name="answer_before")
def answer_before(query: str, lang: str) -> str:
    return query


@observe(name="answer_after", named_inputs=True)
def answer_after(query: str, lang: str) -> str:
    return query


answer_before("how do I return an item?", "en")
answer_after("how do I return an item?", "en")

get_client().flush()

• Binds arguments with inspect.signature; only passed arguments are recorded, defaults are not.
• self / cls are excluded.
• Falls back to the current format if binding fails.
• Default behavior is unchanged.

Discussion: https://github.com/orgs/langfuse/discussions/19377

Type of change

• New feature

Verification

uv run --frozen ruff check .
uv run --frozen mypy langfuse --no-error-summary
uv run --frozen pytest -n auto --dist worksteal tests/unit

Checklist

• I self-reviewed the diff using code_review.md.
• I added or updated tests for behavior changes.

Confidence Score: 4/5

The PR appears safe to merge, with a non-blocking issue where a later cls parameter causes a real input to disappear from traces.

Summary

Adds opt-in named_inputs to @observe.

• Decorated calls can record inputs under their parameter names.

_{Reviews (1) · Last reviewed commit: "feat(observe): add named_inputs option t..." · Reviewed by Greptile}

[claude]

Claude Code Review

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