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Inspect your runnables

Once you create a runnable with LCEL, you may often want to inspect it to get a better sense for what is going on. This notebook covers some methods for doing so.

First, let’s create an example LCEL. We will create one that does retrieval

%pip install --upgrade --quiet  langchain langchain-openai faiss-cpu tiktoken
from langchain_community.vectorstores import FAISS
from langchain_core.output_parsers import StrOutputParser
from langchain_core.prompts import ChatPromptTemplate
from langchain_core.runnables import RunnablePassthrough
from langchain_openai import ChatOpenAI, OpenAIEmbeddings
vectorstore = FAISS.from_texts(
["harrison worked at kensho"], embedding=OpenAIEmbeddings()
)
retriever = vectorstore.as_retriever()

template = """Answer the question based only on the following context:
{context}

Question: {question}
"""
prompt = ChatPromptTemplate.from_template(template)

model = ChatOpenAI()
chain = (
{"context": retriever, "question": RunnablePassthrough()}
| prompt
| model
| StrOutputParser()
)

Get a graph​

You can get a graph of the runnable

chain.get_graph()

While that is not super legible, you can print it to get a display that’s easier to understand

chain.get_graph().print_ascii()
           +---------------------------------+         
| Parallel<context,question>Input |
+---------------------------------+
** **
*** ***
** **
+----------------------+ +-------------+
| VectorStoreRetriever | | Passthrough |
+----------------------+ +-------------+
** **
*** ***
** **
+----------------------------------+
| Parallel<context,question>Output |
+----------------------------------+
*
*
*
+--------------------+
| ChatPromptTemplate |
+--------------------+
*
*
*
+------------+
| ChatOpenAI |
+------------+
*
*
*
+-----------------+
| StrOutputParser |
+-----------------+
*
*
*
+-----------------------+
| StrOutputParserOutput |
+-----------------------+

Get the prompts​

An important part of every chain is the prompts that are used. You can get the prompts present in the chain:

chain.get_prompts()
[ChatPromptTemplate(input_variables=['context', 'question'], messages=[HumanMessagePromptTemplate(prompt=PromptTemplate(input_variables=['context', 'question'], template='Answer the question based only on the following context:\n{context}\n\nQuestion: {question}\n'))])]

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