Refactored example_generator (langchain-ai#8099)

Refactored `example_generator.py`. The same as langchain-ai#7961 
`example_generator.py` is in the root code folder. This creates the
`langchain.example_generator: Example Generator ` group on the API
Reference navigation ToC, on the same level as `Chains` and `Agents`
which is not correct.

Refactoring:
- moved `example_generator.py` content into
`chains/example_generator.py` (not in `utils` because the
`example_generator` has dependencies on other LangChain classes. It also
doesn't work for moving into `utilities/`)
- added the backwards compatibility ref in the original
`example_generator.py`

@hwchase17

libs/langchain/langchain/chains/__init__.py

@@ -26,6 +26,7 @@
     ChatVectorDBChain,
     ConversationalRetrievalChain,
 )
+from langchain.chains.example_generator import generate_example
 from langchain.chains.flare.base import FlareChain
 from langchain.chains.graph_qa.base import GraphQAChain
 from langchain.chains.graph_qa.cypher import GraphCypherQAChain
@@ -84,9 +85,9 @@
     "GraphCypherQAChain",
     "GraphQAChain",
     "GraphSparqlQAChain",
+    "HugeGraphQAChain",
     "HypotheticalDocumentEmbedder",
     "KuzuQAChain",
-    "HugeGraphQAChain",
     "LLMBashChain",
     "LLMChain",
     "LLMCheckerChain",
@@ -95,6 +96,8 @@
     "LLMRouterChain",
     "LLMSummarizationCheckerChain",
     "MapReduceChain",
+    "MapReduceDocumentsChain",
+    "MapRerankDocumentsChain",
     "MultiPromptChain",
     "MultiRetrievalQAChain",
     "MultiRouteChain",
@@ -105,27 +108,26 @@
     "PALChain",
     "QAGenerationChain",
     "QAWithSourcesChain",
+    "ReduceDocumentsChain",
+    "RefineDocumentsChain",
     "RetrievalQA",
     "RetrievalQAWithSourcesChain",
     "RouterChain",
     "SQLDatabaseChain",
     "SQLDatabaseSequentialChain",
     "SequentialChain",
     "SimpleSequentialChain",
+    "StuffDocumentsChain",
     "TransformChain",
     "VectorDBQA",
     "VectorDBQAWithSourcesChain",
+    "create_citation_fuzzy_match_chain",
     "create_extraction_chain",
     "create_extraction_chain_pydantic",
+    "create_qa_with_sources_chain",
+    "create_qa_with_structure_chain",
     "create_tagging_chain",
     "create_tagging_chain_pydantic",
+    "generate_example",
     "load_chain",
-    "create_citation_fuzzy_match_chain",
-    "create_qa_with_structure_chain",
-    "create_qa_with_sources_chain",
-    "StuffDocumentsChain",
-    "MapRerankDocumentsChain",
-    "MapReduceDocumentsChain",
-    "RefineDocumentsChain",
-    "ReduceDocumentsChain",
 ]

libs/langchain/langchain/chains/example_generator.py

@@ -0,0 +1,22 @@
+from typing import List
+
+from langchain.chains.llm import LLMChain
+from langchain.prompts.few_shot import FewShotPromptTemplate
+from langchain.prompts.prompt import PromptTemplate
+from langchain.schema.language_model import BaseLanguageModel
+
+TEST_GEN_TEMPLATE_SUFFIX = "Add another example."
+
+
+def generate_example(
+    examples: List[dict], llm: BaseLanguageModel, prompt_template: PromptTemplate
+) -> str:
+    """Return another example given a list of examples for a prompt."""
+    prompt = FewShotPromptTemplate(
+        examples=examples,
+        suffix=TEST_GEN_TEMPLATE_SUFFIX,
+        input_variables=[],
+        example_prompt=prompt_template,
+    )
+    chain = LLMChain(llm=llm, prompt=prompt)
+    return chain.predict()

libs/langchain/langchain/example_generator.py

@@ -1,23 +1,4 @@
-"""Utility functions for working with prompts."""
-from typing import List
+"""Keep here for backwards compatibility."""
+from langchain.chains.example_generator import generate_example
 
-from langchain.chains.llm import LLMChain
-from langchain.prompts.few_shot import FewShotPromptTemplate
-from langchain.prompts.prompt import PromptTemplate
-from langchain.schema.language_model import BaseLanguageModel
-
-TEST_GEN_TEMPLATE_SUFFIX = "Add another example."
-
-
-def generate_example(
-    examples: List[dict], llm: BaseLanguageModel, prompt_template: PromptTemplate
-) -> str:
-    """Return another example given a list of examples for a prompt."""
-    prompt = FewShotPromptTemplate(
-        examples=examples,
-        suffix=TEST_GEN_TEMPLATE_SUFFIX,
-        input_variables=[],
-        example_prompt=prompt_template,
-    )
-    chain = LLMChain(llm=llm, prompt=prompt)
-    return chain.predict()
+__all__ = ["generate_example"]