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Code Issues 314 Packages Projects Releases 17 Wiki Activity

Default value of state variable not working with reducer function #745

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opened 2026-02-20 17:41:33 -05:00 by yindo · 8 comments
yindo commented 2026-02-20 17:41:33 -05:00
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Originally created by @minki-j on GitHub (Jun 27, 2025).

Checked other resources

  • This is a bug, not a usage question. For questions, please use GitHub Discussions.
  • I added a clear and detailed title that summarizes the issue.
  • I read what a minimal reproducible example is (https://stackoverflow.com/help/minimal-reproducible-example).
  • I included a self-contained, minimal example that demonstrates the issue INCLUDING all the relevant imports. The code run AS IS to reproduce the issue.

Example Code

def extend_list(original: list, new: list):
    original.extend(new)
    return original

OverallState(BaseModel):
    variable: Annotated[list[str], extend_list] = Field(default_factory=lambda: ["default"])

Error Message and Stack Trace (if applicable)

Description

When I set default value for a state variable that has Annotated with a reducer function, the default value is not applied.

System Info

System Information

OS: Darwin
OS Version: Darwin Kernel Version 24.5.0: Tue Apr 22 19:54:43 PDT 2025; root:xnu-11417.121.6~2/RELEASE_ARM64_T8132
Python Version: 3.13.2 (main, Mar 17 2025, 21:26:38) [Clang 20.1.0 ]

Package Information

langchain_core: 0.3.66
langchain: 0.3.26
langsmith: 0.4.2
langchain_anthropic: 0.3.15
langchain_openai: 0.3.25
langchain_text_splitters: 0.3.8
langgraph_sdk: 0.1.70

Optional packages not installed

langserve

Other Dependencies

anthropic<1,>=0.52.0: Installed. No version info available.
async-timeout<5.0.0,>=4.0.0;: Installed. No version info available.
httpx: 0.28.1
httpx>=0.25.2: Installed. No version info available.
jsonpatch<2.0,>=1.33: Installed. No version info available.
langchain-anthropic;: Installed. No version info available.
langchain-aws;: Installed. No version info available.
langchain-azure-ai;: Installed. No version info available.
langchain-cohere;: Installed. No version info available.
langchain-community;: Installed. No version info available.
langchain-core<1.0.0,>=0.3.51: Installed. No version info available.
langchain-core<1.0.0,>=0.3.63: Installed. No version info available.
langchain-core<1.0.0,>=0.3.66: Installed. No version info available.
langchain-deepseek;: Installed. No version info available.
langchain-fireworks;: Installed. No version info available.
langchain-google-genai;: Installed. No version info available.
langchain-google-vertexai;: Installed. No version info available.
langchain-groq;: Installed. No version info available.
langchain-huggingface;: Installed. No version info available.
langchain-mistralai;: Installed. No version info available.
langchain-ollama;: Installed. No version info available.
langchain-openai;: Installed. No version info available.
langchain-perplexity;: Installed. No version info available.
langchain-text-splitters<1.0.0,>=0.3.8: Installed. No version info available.
langchain-together;: Installed. No version info available.
langchain-xai;: Installed. No version info available.
langsmith-pyo3: Installed. No version info available.
langsmith>=0.1.17: Installed. No version info available.
langsmith>=0.3.45: Installed. No version info available.
openai-agents: Installed. No version info available.
openai<2.0.0,>=1.86.0: Installed. No version info available.
opentelemetry-api: Installed. No version info available.
opentelemetry-exporter-otlp-proto-http: Installed. No version info available.
opentelemetry-sdk: Installed. No version info available.
orjson: 3.10.18
orjson>=3.10.1: Installed. No version info available.
packaging: 24.2
packaging<25,>=23.2: Installed. No version info available.
pydantic: 2.11.7
pydantic<3.0.0,>=2.7.4: Installed. No version info available.
pydantic>=2.7.4: Installed. No version info available.
pytest: Installed. No version info available.
PyYAML>=5.3: Installed. No version info available.
requests: 2.32.4
requests-toolbelt: 1.0.0
requests<3,>=2: Installed. No version info available.
rich: Installed. No version info available.
SQLAlchemy<3,>=1.4: Installed. No version info available.
tenacity!=8.4.0,<10.0.0,>=8.1.0: Installed. No version info available.
tiktoken<1,>=0.7: Installed. No version info available.
typing-extensions>=4.7: Installed. No version info available.
zstandard: 0.23.0

Originally created by @minki-j on GitHub (Jun 27, 2025). ### Checked other resources - [x] This is a bug, not a usage question. For questions, please use GitHub Discussions. - [x] I added a clear and detailed title that summarizes the issue. - [x] I read what a minimal reproducible example is (https://stackoverflow.com/help/minimal-reproducible-example). - [x] I included a self-contained, minimal example that demonstrates the issue INCLUDING all the relevant imports. The code run AS IS to reproduce the issue. ### Example Code ```python def extend_list(original: list, new: list): original.extend(new) return original OverallState(BaseModel): variable: Annotated[list[str], extend_list] = Field(default_factory=lambda: ["default"]) ``` ### Error Message and Stack Trace (if applicable) ```shell ``` ### Description When I set default value for a state variable that has Annotated with a reducer function, the default value is not applied. ### System Info System Information ------------------ > OS: Darwin > OS Version: Darwin Kernel Version 24.5.0: Tue Apr 22 19:54:43 PDT 2025; root:xnu-11417.121.6~2/RELEASE_ARM64_T8132 > Python Version: 3.13.2 (main, Mar 17 2025, 21:26:38) [Clang 20.1.0 ] Package Information ------------------- > langchain_core: 0.3.66 > langchain: 0.3.26 > langsmith: 0.4.2 > langchain_anthropic: 0.3.15 > langchain_openai: 0.3.25 > langchain_text_splitters: 0.3.8 > langgraph_sdk: 0.1.70 Optional packages not installed ------------------------------- > langserve Other Dependencies ------------------ > anthropic<1,>=0.52.0: Installed. No version info available. > async-timeout<5.0.0,>=4.0.0;: Installed. No version info available. > httpx: 0.28.1 > httpx>=0.25.2: Installed. No version info available. > jsonpatch<2.0,>=1.33: Installed. No version info available. > langchain-anthropic;: Installed. No version info available. > langchain-aws;: Installed. No version info available. > langchain-azure-ai;: Installed. No version info available. > langchain-cohere;: Installed. No version info available. > langchain-community;: Installed. No version info available. > langchain-core<1.0.0,>=0.3.51: Installed. No version info available. > langchain-core<1.0.0,>=0.3.63: Installed. No version info available. > langchain-core<1.0.0,>=0.3.66: Installed. No version info available. > langchain-deepseek;: Installed. No version info available. > langchain-fireworks;: Installed. No version info available. > langchain-google-genai;: Installed. No version info available. > langchain-google-vertexai;: Installed. No version info available. > langchain-groq;: Installed. No version info available. > langchain-huggingface;: Installed. No version info available. > langchain-mistralai;: Installed. No version info available. > langchain-ollama;: Installed. No version info available. > langchain-openai;: Installed. No version info available. > langchain-perplexity;: Installed. No version info available. > langchain-text-splitters<1.0.0,>=0.3.8: Installed. No version info available. > langchain-together;: Installed. No version info available. > langchain-xai;: Installed. No version info available. > langsmith-pyo3: Installed. No version info available. > langsmith>=0.1.17: Installed. No version info available. > langsmith>=0.3.45: Installed. No version info available. > openai-agents: Installed. No version info available. > openai<2.0.0,>=1.86.0: Installed. No version info available. > opentelemetry-api: Installed. No version info available. > opentelemetry-exporter-otlp-proto-http: Installed. No version info available. > opentelemetry-sdk: Installed. No version info available. > orjson: 3.10.18 > orjson>=3.10.1: Installed. No version info available. > packaging: 24.2 > packaging<25,>=23.2: Installed. No version info available. > pydantic: 2.11.7 > pydantic<3.0.0,>=2.7.4: Installed. No version info available. > pydantic>=2.7.4: Installed. No version info available. > pytest: Installed. No version info available. > PyYAML>=5.3: Installed. No version info available. > requests: 2.32.4 > requests-toolbelt: 1.0.0 > requests<3,>=2: Installed. No version info available. > rich: Installed. No version info available. > SQLAlchemy<3,>=1.4: Installed. No version info available. > tenacity!=8.4.0,<10.0.0,>=8.1.0: Installed. No version info available. > tiktoken<1,>=0.7: Installed. No version info available. > typing-extensions>=4.7: Installed. No version info available. > zstandard: 0.23.0
yindo added the bughelp wanted labels 2026-02-20 17:41:33 -05:00
yindo commented 2026-02-20 17:41:33 -05:00
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@minki-j commented on GitHub (Jun 27, 2025):

Here is Deepwiki's anlaysis on this issue:

https://deepwiki.com/search/when-i-set-default-value-for-a_cd75134c-4404-48e5-a1c1-a25cdda4dd97

@minki-j commented on GitHub (Jun 27, 2025): Here is Deepwiki's anlaysis on this issue: https://deepwiki.com/search/when-i-set-default-value-for-a_cd75134c-4404-48e5-a1c1-a25cdda4dd97
yindo commented 2026-02-20 17:41:33 -05:00
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@minki-j commented on GitHub (Jun 27, 2025):

For those who experience the same issue, here is how to get around this at the moment:

default = ["default_example"]

def extend_list(original: list, new: list):
    if len(original) == 0 and len(new) == 0:
        return default

    original.extend(new)
    return original

When the state is initiated, the reducer function will be triggered with empty lists in this case; You can add the default logic in there.

@minki-j commented on GitHub (Jun 27, 2025): For those who experience the same issue, here is how to get around this at the moment: ```python default = ["default_example"] def extend_list(original: list, new: list): if len(original) == 0 and len(new) == 0: return default original.extend(new) return original ``` When the state is initiated, the reducer function will be triggered with empty lists in this case; You can add the default logic in there.
yindo commented 2026-02-20 17:41:33 -05:00
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@sydney-runkle commented on GitHub (Jun 27, 2025):

Can repro this, thanks for the report! PRs welcome with a fix for this.

@sydney-runkle commented on GitHub (Jun 27, 2025): Can repro this, thanks for the report! PRs welcome with a fix for this.
yindo commented 2026-02-20 17:41:33 -05:00
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@hemhemoh commented on GitHub (Jul 1, 2025):

Hello @sydney-runkle, I would like to work on this.

@hemhemoh commented on GitHub (Jul 1, 2025): Hello @sydney-runkle, I would like to work on this.
yindo commented 2026-02-20 17:41:33 -05:00
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@kailip commented on GitHub (Jul 17, 2025):

Hello. I can confirm that the issue is still there in a newest release of langgraph. Could this issue be re-opened?

@kailip commented on GitHub (Jul 17, 2025): Hello. I can confirm that the issue is still there in a newest release of langgraph. Could this issue be re-opened?
yindo commented 2026-02-20 17:41:33 -05:00
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@chitralputhran commented on GitHub (Jul 31, 2025):

Hi @minki-j @sydney-runkle,

Submitted a PR #5789 that addresses the issue regarding Pydantic default values not working with reducer functions.
Would appreciate your feedback and testing on the PR.

Thanks for reporting this bug!

@chitralputhran commented on GitHub (Jul 31, 2025): Hi @minki-j @sydney-runkle, Submitted a PR #5789 that addresses the issue regarding Pydantic default values not working with reducer functions. Would appreciate your feedback and testing on the PR. Thanks for reporting this bug!
yindo commented 2026-02-20 17:41:33 -05:00
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@hoppiesbunny commented on GitHub (Nov 26, 2025):

+1, bumping this up. could we help to merge the PR in? I'm experiencing this bug too @sydney-runkle @minki-j

@hoppiesbunny commented on GitHub (Nov 26, 2025): +1, bumping this up. could we help to merge the PR in? I'm experiencing this bug too @sydney-runkle @minki-j
yindo commented 2026-02-20 17:41:33 -05:00
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@antoinegar commented on GitHub (Jan 7, 2026):

+1, is there any clean way to set up a default value while using a reducer @sydney-runkle @minki-j?

@antoinegar commented on GitHub (Jan 7, 2026): +1, is there any clean way to set up a default value while using a reducer @sydney-runkle @minki-j?
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Reference: langchain-ai/langgraph#745
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