# Bug Report: langchain-docling Pydantic v2 Compatibility Issue

[ajithpaugustine]

Checked other resources

• This is a bug, not a usage question.
• I added a clear and descriptive title that summarizes this issue.
• I used the GitHub search to find a similar question and didn't find it.
• I am sure that this is a bug in LangChain rather than my code.
• The bug is not resolved by updating to the latest stable version of LangChain (or the specific integration package).
• This is not related to the langchain-community package.
• I posted a self-contained, minimal, reproducible example. A maintainer can copy it and run it AS IS.

Package (Required)

• langchain
• langchain-openai
• langchain-anthropic
• langchain-classic
• langchain-core
• langchain-model-profiles
• langchain-tests
• langchain-text-splitters
• langchain-chroma
• langchain-deepseek
• langchain-exa
• langchain-fireworks
• langchain-groq
• langchain-huggingface
• langchain-mistralai
• langchain-nomic
• langchain-ollama
• langchain-openrouter
• langchain-perplexity
• langchain-qdrant
• langchain-xai
• Other / not sure / general

Related Issues / PRs

No response

Reproduction Steps / Example Code (Python)

from langchain_docling import DoclingLoader

def main():
    FILE_PATH = ["https://arxiv.org/pdf/2408.09869"]  # Docling Technical Report
    
    loader = DoclingLoader(file_path=FILE_PATH)
    docs = loader.load()

    print(f"Loaded {len(docs)} documents")
    print(docs[0].page_content[:500])  # Print first 500 characters

if __name__ == "__main__":
    main()

Error Message and Stack Trace (if applicable)

File "d:\arvix_benchmark\venv\lib\site-packages\docling_core\types\__init__.py", line 3, in <module>
    from docling_core.types.doc.document import DoclingDocument
  File "d:\arvix_benchmark\venv\lib\site-packages\docling_core\types\doc\__init__.py", line 4, in <module>
    from .document import (
  File "d:\arvix_benchmark\venv\lib\site-packages\docling_core\types\doc\document.py", line 49, in <module>
    from docling_core.search.package import VERSION_PATTERN
  File "d:\arvix_benchmark\venv\lib\site-packages\docling_core\search\package.py", line 17, in <module>
    class Package(BaseModel, extra="forbid"):
  File "d:\arvix_benchmark\venv\lib\site-packages\docling_core\search\package.py", line 24, in Package
    version: Annotated[str, StringConstraints(strict=True, pattern=VERSION_PATTERN)] = importlib.metadata.version(
TypeError: StringConstraints() takes no arguments

Description

Bug Report: langchain-docling Pydantic v2 Compatibility Issue

Summary

langchain-docling fails to import with a TypeError: StringConstraints() takes no arguments when using current versions of docling-core and Pydantic v2.

Environment

• Python: 3.9.7
• langchain-docling: 1.1.0
• docling: 2.69.1
• docling-core: 2.60.1
• pydantic: 2.12.5
• OS: Windows 10

Error Trace

Traceback (most recent call last):
  File "D:\arvix_benchmark\load.py", line 1, in <module>
    from langchain_docling import DoclingLoader
  File "D:\arvix_benchmark\venv\lib\site-packages\langchain_docling\__init__.py", line 7, in <module>
    from langchain_docling.loader import DoclingLoader
  File "D:\arvix_benchmark\venv\lib\site-packages\langchain_docling\loader.py", line 12, in <module>
    from docling.chunking import BaseChunk, BaseChunker, HybridChunker
  ...
  File "D:\arvix_benchmark\venv\lib\site-packages\docling_core\search\package.py", line 17, in <module>
    class Package(BaseModel, extra="forbid"):
  File "D:\arvix_benchmark\venv\lib\site-packages\docling_core\search\package.py", line 24, in Package
    version: Annotated[str, StringConstraints(strict=True, pattern=VERSION_PATTERN)] = ...
TypeError: StringConstraints() takes no arguments

Root Cause

In docling_core/search/package.py line 24, the code calls:

StringConstraints(strict=True, pattern=VERSION_PATTERN)

However, in Pydantic v2.12.5, StringConstraints() does not accept positional/keyword arguments in this way. The correct syntax for Pydantic v2 is:

StringConstraints(min_length=1, pattern=VERSION_PATTERN)
# or use Field with constraints

Steps to Reproduce

1. Create a Python 3.9+ environment
2. Install: pip install langchain-docling pydantic>=2.0
3. Try to import: from langchain_docling import DoclingLoader
4. Error occurs

Expected Behavior

langchain-docling should import successfully and be usable with Pydantic v2.x

Actual Behavior

Import fails with TypeError: StringConstraints() takes no arguments

Suggested Fix

Update docling-core to use Pydantic v2 syntax for StringConstraints, or pin pydantic to a compatible version in setup.py/pyproject.toml.

Workaround (if available)

• Downgrade to older versions: pip install docling-core==2.48.0 docling==2.18.0
• Or use an alternative document loader

---

Report this to:

• https://github.com/langchain-ai/langchain-docling?target=https://github.com (or relevant repo)

System Info

System Information

OS: Windows
OS Version: 10.0.22631
Python Version: 3.9.7 (default, Sep 16 2021, 16:59:28) [MSC v.1916 64 bit (AMD64)]

Package Information

langchain_core: 0.3.83
langchain: 0.3.27
langsmith: 0.4.37
langchain_docling: 1.1.0
langchain_text_splitters: 0.3.11

Optional packages not installed

langserve

Other Dependencies

async-timeout<5.0.0,>=4.0.0;: Installed. No version info available.
claude-agent-sdk>=0.1.0;: Installed. No version info available.
docling~=2.18: Installed. No version info available.
httpx<1,>=0.23.0: Installed. No version info available.
jsonpatch<2.0.0,>=1.33.0: 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,>=0.3.72: Installed. No version info available.
langchain-core<2.0.0,>=0.3.75: Installed. No version info available.
langchain-core~=0.3.19: 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,>=0.3.9: Installed. No version info available.
langchain-together;: Installed. No version info available.
langchain-xai;: Installed. No version info available.
langsmith-pyo3>=0.1.0rc2;: Installed. No version info available.
langsmith<1.0.0,>=0.3.45: Installed. No version info available.
langsmith>=0.1.17: Installed. No version info available.
openai-agents>=0.0.3;: Installed. No version info available.
opentelemetry-api>=1.30.0;: Installed. No version info available.
opentelemetry-exporter-otlp-proto-http>=1.30.0;: Installed. No version info available.
opentelemetry-sdk>=1.30.0;: Installed. No version info available.
orjson>=3.9.14;: Installed. No version info available.
packaging<26.0.0,>=23.2.0: Installed. No version info available.
packaging>=23.2: Installed. No version info available.
pydantic<3,>=1: Installed. No version info available.
pydantic<3.0.0,>=2.7.4: Installed. No version info available.
pytest>=7.0.0;: Installed. No version info available.
PyYAML<7.0.0,>=5.3.0: Installed. No version info available.
PyYAML>=5.3: Installed. No version info available.
requests-toolbelt>=1.0.0: Installed. No version info available.
requests<3,>=2: Installed. No version info available.
requests>=2.0.0: Installed. No version info available.
rich>=13.9.4;: 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.
typing-extensions<5.0.0,>=4.7.0: Installed. No version info available.
uuid-utils<1.0,>=0.12.0: Installed. No version info available.
vcrpy>=7.0.0;: Installed. No version info available.
zstandard>=0.23.0: Installed. No version info available.

[xXMrNidaXx]

Root Cause Analysis

This is a Pydantic v1 vs v2 compatibility issue in docling-core, not directly in langchain-docling.

The error occurs because StringConstraints in Pydantic v2 is a class that accepts keyword arguments, but the code is being called with Pydantic v1 semantics where StringConstraints() takes no arguments.

Two scenarios cause this:

1. Mixed Pydantic versions: docling-core was written for Pydantic v2, but you have v1 installed (possibly pinned by another dependency)

2. Version mismatch: Older docling-core expects Pydantic v1, but you have v2

Workarounds

Option 1: Force Pydantic v2

pip install "pydantic>=2.0,<3.0" --force-reinstall
pip install langchain-docling --no-deps
pip install docling-core

Option 2: Check your constraints

pip list | grep pydantic
# Should show pydantic 2.x for modern docling-core

Option 3: Use pip constraint file
Create constraints.txt:

pydantic>=2.0,<3.0

Then:

pip install langchain-docling -c constraints.txt

For maintainers

Consider adding an explicit Pydantic v2 pin in langchain-docling's dependencies:

"pydantic>=2.0,<3.0"

This would fail-fast during install rather than at runtime.

---

Corey Nida | RevolutionAI — We help teams ship AI products without the infrastructure headaches.

[keenborder786]

ajithpaugustine Feel like an appropriate place to open the issue is at the following repo: https://github.com/docling-project/docling-langchain?target=https://github.com

[ajithpaugustine]

thanks Corey nida (@xXMrNidaXx) for the reply. I tried those but the issue i am facing was in importing in the library itself. i tried forcing pydantic v2 but still the issue persists.

As Mohammad Mohtashim (@keenborder786) has pointed it out let me open an issue with docling repo rather than langchain.

Thank you guys!

[keenborder786]

ajithpaugustine can you close the issue here?