feat(langchain): add LangChain 1.x compatibility with fallback patterns

Add try/except fallback patterns in examples to support both LangChain
0.x and 1.x. When using LangChain 1.x, legacy Chain features are
imported from langchain-classic package with helpful error messages.

This allows examples to work seamlessly across LangChain versions
without requiring code changes from users.

- Add fallback imports for RetrievalQA, embeddings, text splitters,
vectorstores
- Provide clear error messages directing users to install
langchain-classic

Author: Pouyanpi

examples/configs/rag/custom_rag_output_rails/config.py

@@ -13,9 +13,9 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-from langchain.prompts import PromptTemplate
 from langchain_core.language_models.llms import BaseLLM
 from langchain_core.output_parsers import StrOutputParser
+from langchain_core.prompts import PromptTemplate
 
 from nemoguardrails import LLMRails
 from nemoguardrails.actions.actions import ActionResult

examples/configs/rag/multi_kb/config.py

@@ -21,10 +21,24 @@
 import pandas as pd
 import torch
 from gpt4pandas import GPT4Pandas
-from langchain.chains import RetrievalQA
-from langchain.embeddings import HuggingFaceEmbeddings
-from langchain.text_splitter import CharacterTextSplitter
-from langchain.vectorstores import FAISS
+
+try:
+    from langchain.chains import RetrievalQA
+    from langchain.embeddings import HuggingFaceEmbeddings
+    from langchain.text_splitter import CharacterTextSplitter
+    from langchain.vectorstores import FAISS
+except ImportError:
+    try:
+        from langchain_classic.chains import RetrievalQA
+        from langchain_classic.embeddings import HuggingFaceEmbeddings
+        from langchain_classic.text_splitter import CharacterTextSplitter
+        from langchain_classic.vectorstores import FAISS
+    except ImportError as e:
+        raise ImportError(
+            "Failed to import from langchain. If you're using LangChain >= 1.0.0, "
+            "please install langchain-classic: pip install langchain-classic"
+        ) from e
+
 from langchain_core.language_models.llms import BaseLLM
 from transformers import AutoModelForCausalLM, AutoTokenizer, pipeline
 

examples/configs/rag/multi_kb/tabular_llm.py

@@ -13,14 +13,13 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-import asyncio
 from typing import Any, Dict, List, Optional
 
-from langchain.callbacks.manager import (
+from langchain_core.callbacks.manager import (
     AsyncCallbackManagerForLLMRun,
     CallbackManagerForLLMRun,
 )
-from langchain.llms.base import LLM
+from langchain_core.language_models.llms import BaseLLM
 
 
 def query_tabular_data(usr_query: str, gpt: any, raw_data_frame: any):
@@ -58,7 +57,7 @@ def query_tabular_data(usr_query: str, gpt: any, raw_data_frame: any):
     return out, d2.to_string()
 
 
-class TabularLLM(LLM):
+class TabularLLM(BaseLLM):
     """LLM wrapping for GPT4Pandas."""
 
     model: str = ""

examples/configs/rag/pinecone/config.py

@@ -18,10 +18,24 @@
 from typing import Optional
 
 import pinecone
-from langchain.chains import RetrievalQA
-from langchain.docstore.document import Document
-from langchain.embeddings.openai import OpenAIEmbeddings
-from langchain.vectorstores import Pinecone
+
+try:
+    from langchain.chains import RetrievalQA
+    from langchain.docstore.document import Document
+    from langchain.embeddings.openai import OpenAIEmbeddings
+    from langchain.vectorstores import Pinecone
+except ImportError:
+    try:
+        from langchain_classic.chains import RetrievalQA
+        from langchain_classic.docstore.document import Document
+        from langchain_classic.embeddings.openai import OpenAIEmbeddings
+        from langchain_classic.vectorstores import Pinecone
+    except ImportError as e:
+        raise ImportError(
+            "Failed to import from langchain. If you're using LangChain >= 1.0.0, "
+            "please install langchain-classic: pip install langchain-classic"
+        ) from e
+
 from langchain_core.language_models.llms import BaseLLM
 
 from nemoguardrails import LLMRails

examples/scripts/langchain/experiments.py

@@ -15,8 +15,18 @@
 
 import os
 
-from langchain.chains import LLMMathChain
-from langchain.prompts import ChatPromptTemplate
+try:
+    from langchain.chains import LLMMathChain
+except ImportError:
+    try:
+        from langchain_classic.chains import LLMMathChain
+    except ImportError as e:
+        raise ImportError(
+            "Failed to import LLMMathChain. If you're using LangChain >= 1.0.0, "
+            "please install langchain-classic: pip install langchain-classic"
+        ) from e
+
+from langchain_core.prompts import ChatPromptTemplate
 from langchain_core.tools import Tool
 from langchain_openai.chat_models import ChatOpenAI
 from pydantic import BaseModel, Field