chore(langchain): Refactor the string concatenation to use the more efficient .join() m…

[湛露先生 (zhanluxianshen)]

Refactor the string concatenation to use the more efficient .join() method.

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1 Skipped Deployment

Project	Deployment	Preview	Comments	Updated (UTC)
langchain	Ignored	Preview		Sep 12, 2025 8:30am

[codspeed-hq]

CodSpeed WallTime Performance Report

Merging #32915 will degrade performances by 16.1%

_{Comparing zhanluxianshen:clean-str-appends (649af3e) with master (649d8a8)}

⚠️ 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

❌ 9 regressions
✅ 4 untouched

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	BASE	HEAD	Change
❌	test_import_time[CallbackManager]	446.4 ms	525 ms	-14.98%
❌	test_import_time[HumanMessage]	211.3 ms	244.2 ms	-13.46%
❌	test_import_time[InMemoryRateLimiter]	164.9 ms	183.6 ms	-10.2%
❌	test_import_time[InMemoryVectorStore]	613.4 ms	717.8 ms	-14.54%
❌	test_import_time[LangChainTracer]	425.3 ms	493.7 ms	-13.84%
❌	test_import_time[PydanticOutputParser]	544.4 ms	637.1 ms	-14.55%
❌	test_import_time[RunnableLambda]	476.7 ms	539.8 ms	-11.69%
❌	test_import_time[Runnable]	477.9 ms	567.7 ms	-15.81%
❌	test_import_time[tool]	508.3 ms	605.9 ms	-16.1%

[codspeed-hq]

CodSpeed Instrumentation Performance Report

Merging #32915 will not alter performance

_{Comparing zhanluxianshen:clean-str-appends (649af3e) with master (649d8a8)}

Summary

✅ 14 untouched

[Eugene Yurtsev (eyurtsev)]

湛露先生 (@zhanluxianshen) thanks for taking the time to make a contribution. For optimizations we would generally want to see evidence that things make a difference. In this case, this optimization does not make any meaningful difference so we won't accept it.

I would suggest taking the patch and some of this information and discussing with chat gpt or claude and getting some critique in terms of what optimizations are meaningful or not :)