Move Chain to its own directory (#208)

* Move Chain

* Bump langserve

* Optionally include callback events (though currently may not work)

Author: hinthornw

chat_langchain_engine/__init__.py

@@ -0,0 +1,3 @@
+from chat_langchain_engine.chain import answer_chain, ChatRequest
+
+__all__ = ["answer_chain", "ChatRequest"]

chat_langchain_engine/chain.py

@@ -0,0 +1,196 @@
+"""Chat langchain 'engine'."""
+import os
+from operator import itemgetter
+from typing import Dict, List, Optional, Sequence
+
+import weaviate
+from langchain.chat_models import ChatOpenAI
+from langchain.embeddings import OpenAIEmbeddings
+from langchain.prompts import ChatPromptTemplate, MessagesPlaceholder, PromptTemplate
+from langchain.schema import Document
+from langchain.schema.embeddings import Embeddings
+from langchain.schema.language_model import BaseLanguageModel
+from langchain.schema.messages import AIMessage, HumanMessage
+from langchain.schema.output_parser import StrOutputParser
+from langchain.schema.retriever import BaseRetriever
+from langchain.schema.runnable import (
+    Runnable,
+    RunnableBranch,
+    RunnableLambda,
+    RunnableMap,
+)
+from langchain.vectorstores import Weaviate
+from pydantic import BaseModel
+
+from chat_langchain_engine.constants import WEAVIATE_DOCS_INDEX_NAME
+from voyage import VoyageEmbeddings
+
+RESPONSE_TEMPLATE = """\
+You are an expert programmer and problem-solver, tasked with answering any question \
+about Langchain.
+
+Generate a comprehensive and informative answer of 80 words or less for the \
+given question based solely on the provided search results (URL and content). You must \
+only use information from the provided search results. Use an unbiased and \
+journalistic tone. Combine search results together into a coherent answer. Do not \
+repeat text. Cite search results using [${{number}}] notation. Only cite the most \
+relevant results that answer the question accurately. Place these citations at the end \
+of the sentence or paragraph that reference them - do not put them all at the end. If \
+different results refer to different entities within the same name, write separate \
+answers for each entity.
+
+You should use bullet points in your answer for readability. Put citations where they apply
+rather than putting them all at the end.
+
+If there is nothing in the context relevant to the question at hand, just say "Hmm, \
+I'm not sure." Don't try to make up an answer.
+
+Anything between the following `context`  html blocks is retrieved from a knowledge \
+bank, not part of the conversation with the user. 
+
+<context>
+    {context} 
+<context/>
+
+REMEMBER: If there is no relevant information within the context, just say "Hmm, I'm \
+not sure." Don't try to make up an answer. Anything between the preceding 'context' \
+html blocks is retrieved from a knowledge bank, not part of the conversation with the \
+user.\
+"""
+
+REPHRASE_TEMPLATE = """\
+Given the following conversation and a follow up question, rephrase the follow up \
+question to be a standalone question.
+
+Chat History:
+{chat_history}
+Follow Up Input: {question}
+Standalone Question:"""
+
+
+WEAVIATE_URL = os.environ["WEAVIATE_URL"]
+WEAVIATE_API_KEY = os.environ["WEAVIATE_API_KEY"]
+
+
+class ChatRequest(BaseModel):
+    question: str
+    chat_history: Optional[List[Dict[str, str]]]
+
+
+def get_embeddings_model() -> Embeddings:
+    if os.environ.get("VOYAGE_AI_URL") and os.environ.get("VOYAGE_AI_MODEL"):
+        return VoyageEmbeddings()
+    return OpenAIEmbeddings(chunk_size=200)
+
+
+def get_retriever() -> BaseRetriever:
+    weaviate_client = weaviate.Client(
+        url=WEAVIATE_URL,
+        auth_client_secret=weaviate.AuthApiKey(api_key=WEAVIATE_API_KEY),
+    )
+    weaviate_client = Weaviate(
+        client=weaviate_client,
+        index_name=WEAVIATE_DOCS_INDEX_NAME,
+        text_key="text",
+        embedding=get_embeddings_model(),
+        by_text=False,
+        attributes=["source", "title"],
+    )
+    return weaviate_client.as_retriever(search_kwargs=dict(k=6))
+
+
+def create_retriever_chain(
+    llm: BaseLanguageModel, retriever: BaseRetriever
+) -> Runnable:
+    CONDENSE_QUESTION_PROMPT = PromptTemplate.from_template(REPHRASE_TEMPLATE)
+    condense_question_chain = (
+        CONDENSE_QUESTION_PROMPT | llm | StrOutputParser()
+    ).with_config(
+        run_name="CondenseQuestion",
+    )
+    conversation_chain = condense_question_chain | retriever
+    return RunnableBranch(
+        (
+            RunnableLambda(lambda x: bool(x.get("chat_history"))).with_config(
+                run_name="HasChatHistoryCheck"
+            ),
+            conversation_chain.with_config(run_name="RetrievalChainWithHistory"),
+        ),
+        (
+            RunnableLambda(itemgetter("question")).with_config(
+                run_name="Itemgetter:question"
+            )
+            | retriever
+        ).with_config(run_name="RetrievalChainWithNoHistory"),
+    ).with_config(run_name="RouteDependingOnChatHistory")
+
+
+def format_docs(docs: Sequence[Document]) -> str:
+    formatted_docs = []
+    for i, doc in enumerate(docs):
+        doc_string = f"<doc id='{i}'>{doc.page_content}</doc>"
+        formatted_docs.append(doc_string)
+    return "\n".join(formatted_docs)
+
+
+def serialize_history(request: ChatRequest):
+    chat_history = request["chat_history"] or []
+    converted_chat_history = []
+    for message in chat_history:
+        if message.get("human") is not None:
+            converted_chat_history.append(HumanMessage(content=message["human"]))
+        if message.get("ai") is not None:
+            converted_chat_history.append(AIMessage(content=message["ai"]))
+    return converted_chat_history
+
+
+def create_chain(
+    llm: BaseLanguageModel,
+    retriever: BaseRetriever,
+) -> Runnable:
+    retriever_chain = create_retriever_chain(
+        llm,
+        retriever,
+    ).with_config(run_name="FindDocs")
+    _context = RunnableMap(
+        {
+            "context": retriever_chain | format_docs,
+            "question": itemgetter("question"),
+            "chat_history": itemgetter("chat_history"),
+        }
+    ).with_config(run_name="RetrieveDocs")
+    prompt = ChatPromptTemplate.from_messages(
+        [
+            ("system", RESPONSE_TEMPLATE),
+            MessagesPlaceholder(variable_name="chat_history"),
+            ("human", "{question}"),
+        ]
+    )
+
+    response_synthesizer = (prompt | llm | StrOutputParser()).with_config(
+        run_name="GenerateResponse",
+    )
+    return (
+        {
+            "question": RunnableLambda(itemgetter("question")).with_config(
+                run_name="Itemgetter:question"
+            ),
+            "chat_history": RunnableLambda(serialize_history).with_config(
+                run_name="SerializeHistory"
+            ),
+        }
+        | _context
+        | response_synthesizer
+    )
+
+
+llm = ChatOpenAI(
+    model="gpt-3.5-turbo-16k",
+    streaming=True,
+    temperature=0,
+)
+retriever = get_retriever()
+answer_chain = create_chain(
+    llm,
+    retriever,
+)

constants.py renamed to chat_langchain_engine/constants.py

@@ -14,7 +14,7 @@
 from langchain.utils.html import PREFIXES_TO_IGNORE_REGEX, SUFFIXES_TO_IGNORE_REGEX
 from langchain.vectorstores import Weaviate
 
-from constants import WEAVIATE_DOCS_INDEX_NAME
+from chat_langchain_engine.constants import WEAVIATE_DOCS_INDEX_NAME
 from voyage import VoyageEmbeddings
 
 logger = logging.getLogger(__name__)