langchain[patch]: Revert 20794 until 0.2 release (#21257)

PR of 2079 was already released as part of 0.1.17rc.


Issue for 0.2 release:
https://github.com/langchain-ai/langchain/issues/21080

libs/langchain/langchain/chains/flare/base.py

@@ -5,6 +5,7 @@ from abc import abstractmethod
 from typing import Any, Dict, List, Optional, Sequence, Tuple
 
 import numpy as np
+from langchain_community.llms.openai import OpenAI
 from langchain_core.callbacks import (
     CallbackManagerForChainRun,
 )
@@ -55,7 +56,11 @@ class _ResponseChain(LLMChain):
 class _OpenAIResponseChain(_ResponseChain):
     """Chain that generates responses from user input and context."""
 
-    llm: BaseLanguageModel
+    llm: OpenAI = Field(
+        default_factory=lambda: OpenAI(
+            max_tokens=32, model_kwargs={"logprobs": 1}, temperature=0
+        )
+    )
 
     def _extract_tokens_and_log_probs(
         self, generations: List[Generation]
@@ -113,7 +118,7 @@ class FlareChain(Chain):
 
     question_generator_chain: QuestionGeneratorChain
     """Chain that generates questions from uncertain spans."""
-    response_chain: _ResponseChain
+    response_chain: _ResponseChain = Field(default_factory=_OpenAIResponseChain)
     """Chain that generates responses from user input and context."""
     output_parser: FinishedOutputParser = Field(default_factory=FinishedOutputParser)
     """Parser that determines whether the chain is finished."""
@@ -250,14 +255,6 @@ class FlareChain(Chain):
         Returns:
             FlareChain class with the given language model.
         """
-        try:
-            from langchain_openai import OpenAI
-        except ImportError:
-            raise ImportError(
-                "OpenAI is required for FlareChain. "
-                "Please install langchain-openai."
-                "pip install langchain-openai"
-            )
         question_gen_chain = QuestionGeneratorChain(llm=llm)
         response_llm = OpenAI(
             max_tokens=max_generation_len, model_kwargs={"logprobs": 1}, temperature=0