langchain/docs/extras/modules/callbacks/filecallbackhandler.ipynb

Logging to file

This example shows how to print logs to file. It shows how to use the FileCallbackHandler, which does the same thing as StdOutCallbackHandler, but instead writes the output to file. It also uses the loguru library to log other outputs that are not captured by the handler.

In [1]:

from loguru import logger

from langchain.callbacks import FileCallbackHandler
from langchain.chains import LLMChain
from langchain.llms import OpenAI
from langchain.prompts import PromptTemplate

logfile = "output.log"

logger.add(logfile, colorize=True, enqueue=True)
handler = FileCallbackHandler(logfile)

llm = OpenAI()
prompt = PromptTemplate.from_template("1 + {number} = ")

# 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 = LLMChain(llm=llm, prompt=prompt, callbacks=[handler], verbose=True)
answer = chain.run(number=2)
logger.info(answer)

> Entering new LLMChain chain...
Prompt after formatting:
1 + 2 = 

2023-06-01 18:36:38.929 | INFO     | __main__:<module>:20 - 

3

> Finished chain.

Now we can open the file output.log to see that the output has been captured.

In [2]:

!pip install ansi2html > /dev/null

In [3]:

from IPython.display import display, HTML
from ansi2html import Ansi2HTMLConverter

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