File logging
LangChain provides the FileCallbackHandler to write logs to a file.
The FileCallbackHandler is similar to the
StdOutCallbackHandler, but instead of
printing logs to standard output it writes logs to a file.
We see how to use the FileCallbackHandler in this example.
Additionally we use the StdOutCallbackHandler to print logs to the
standard output. It also uses the loguru library to log other outputs
that are not captured by the handler.
from langchain_core.callbacks import FileCallbackHandler, StdOutCallbackHandler
from langchain_core.prompts import PromptTemplate
from langchain_openai import OpenAI
from loguru import logger
logfile = "output.log"
logger.add(logfile, colorize=True, enqueue=True)
handler_1 = FileCallbackHandler(logfile)
handler_2 = StdOutCallbackHandler()
prompt = PromptTemplate.from_template("1 + {number} = ")
model = OpenAI()
# this chain will both print to stdout (because verbose=True) and write to 'output.log'
# if verbose=False, the FileCallbackHandler will still write to 'output.log'
chain = prompt | model
response = chain.invoke({"number": 2}, {"callbacks": [handler_1, handler_2]})
logger.info(response)
> Entering new LLMChain chain...
Prompt after formatting:
1 + 2 =
> Finished chain.
2023-06-01 18:36:38.929 | INFO | __main__:<module>:20 -
3
Now we can open the file output.log to see that the output has been
captured.
%pip install --upgrade --quiet ansi2html > /dev/null
from ansi2html import Ansi2HTMLConverter
from IPython.display import HTML, display
with open("output.log", "r") as f:
content = f.read()
conv = Ansi2HTMLConverter()
html = conv.convert(content, full=True)
display(HTML(html))
> Entering new LLMChain chain... Prompt after formatting: 1 + 2 = > Finished chain. 2023-06-01 18:36:38.929 | INFO | __main__:<module>:20 - 3