Langchain Law

A Python library for classifying legal judgements using the langchain library and OpenAI.

Example use: On this case: https://www.caselaw.nsw.gov.au/decision/54a004453004262463c948bc

Installation

Prerequisites: Git and Poetry

Get a copy of the repo using git clone and then set up your Python environment and dependencies with poetry install:

git clone git@github.com:Sydney-Informatics-Hub/langchainlaw.git
cd langchainlaw
poetry install

Command Line

The classify command will classify a directory containing judgments in the json format output by the nswcaselaw library, caching the LLM responses and writing the results out to a spreadsheet. It is configured using a JSON file with the following format:

{
    "providers": {
        "OpenAI": {
            "api_key": "SECRET_GOES_HERE",
            "organization": "ORG_KEY_GOES_HERE",
            "model": "gpt-4o"
        }
    },
    "provider": "OpenAI",
    "temperature": 0,
    "rate_limit": 15,
    "prompts": "./tests/sample_prompts.xlsx",
    "input": "./input/",
    "output": "./output/results.xlsx",
    "cache": "./output/cache",
    "test_prompts": "./outputs/test_prompts.txt"
}

You should make a copy of config.example.json as config.json before you add your API keys.

The configurations for files and directories for input and output are as follows:

• prompts: spreadsheet with the prompt questions - see below for format
• input: all .json files here will be read as cases
• output: results are written to this spreadsheet, one line per case
• cache: a directory will be created in this for each case, and results from the LLM for each prompt will be written to it in a file with that prompt's name.
• test_prompts: text file to write all prompts when using --test

To run the classify command, use poetry run:

poetry run classify --config config.json

If you re-run the classifier, it will look in the cache for each case / prompt combination and return a cached result if it exists, rather than going to the LLM. To force the classifier to go to the LLM even if a cached result exists, use the --no-cache flag.

Command line options for the command-line tool:

• --config FILE - specify the JSON config file
• --test - generate prompts and write them to the test_prompts file but don't call the LLM for classification
• --case CASEFILE - run the classifier for a single case, specified by its JSON filename
• --prompt PROMPT - run the classifier for only one prompt, specified by its name in the spreadsheet
• --no-cache - call the LLM even if there is a cached result for a prompt

GPT-4o sometimes adds 'notes' to its output even when instructed to return JSON - these notes are also saved to the cache, although they are ignored when building the results spreadsheet.

API

You can use the Classifier object in your own Python scripts or notebooks:

from langchainlaw.langchainlaw import Classifier
from pandas import DataFrame
from pathlib import Path
import json

with open("config.json", "r") as cfh:
	config = json.load(cfh)

classifier = Classifier(config)

classifier.load_prompts(config["prompts"])

# classify a single case

output = classifier.classify("cases/123456789abcdef0.json")

# iterate over a directory and build a dataframe

results = []
for casefile in Path("cases").glob("*.json"):
	output = classifier.classify(casefile)
	results.append(classifier.as_dict(output))
df = DataFrame(results)

See the sample notebook for an example of using langchainlaw from a Jupyter notebook. To run this notebook locally use the following poetry command:

poetry run jupyter notebook notebook.ipynb

The notebook assumes that you have a config.json file with your OpenAI keys in the root directory of the repo.

Prompts

Prompts are configured using an Excel spreadsheet - here is an example

system

Cell A2 contains the system prompt: this is the message which is sent to the LLM as a System prompt and is used to set the persona for the rest of the chat. For example:

You are a legal research assistant helping an academic researcher to answer questions about a public judgment of a decision in inheritance law. You will be provided with the judgment and metadata as a JSON document. Please answer the questions about the judgment based only on information contained in the judgment. Where your answer comes from a specific paragraph in the judgment, provide the paragraph number as part of your answer. If you cannot answer any of the questions based on the judgment or metadata, do not make up
  information, but instead write ""answer not found"""

intro

Cell A2 contains the template which is used to start each chat message. The string {judgment} is expanded to the JSON of the case being classified.

Based on the metadata and judgment in the following JSON {judgment}, 

prompts

Each request to the LLM is a set of related questions configured with the prompts worksheet. The columns of this sheet are:

Prompt_name	return_type	repeats	prompt_question	return_instructions	additional_instructions	fields	question_description	example
prompt id	json or json_multiple	repeat json_multiple this many times	top-level question	description of JSON structure	additional instructions if required	unique field name for each sub-question	text of the sub-question	example answer

For example, in the sample spreadsheet, the prompt dates has the following spreadsheet values:

Prompt_name	return_type	repeats	prompt_question	return_instructions	additional_instructions	fields	question_description	example
dates	json		answer the following questions about the case:	Return your answer as a JSON object, following this example:		filing_date	What is the filing date? DD/MM/YYYY	5/6/2010
dates						interlocutory	Does this judgment concern an interlocutory application? Answer "yes", "no" or "unclear"	yes
dates						interlocutory_date	If the judgment concerns an interlocutory application, what was the date of the application? DD/MM/YYYY	4/3/2010

From these, the classifier will build the following prompt:

  answer the following questions about the case:

  Q1: what is the filing date? DD/MM/YYYY
  Q2: does this judgment concern an interlocutory application? Answer "yes", "no" or "unclear" 
  Q3: if the judgment concerns an interlocutory application, what was the date of the application? DD/MM/YYYY

  Return your answer as a JSON object, following this example:
    {{
      "filing_date": "5/6/2010",
      "interlocutory": "yes",
      "interlocutory_date": "4/3/2010"
    }}

Note that the example JSON is constructed automatically from the example answers in the "example" column.

Acknowledgements

This project is partially funded by a 2022 University of Sydney Research Accelerator (SOAR) Prize awarded to Ben Chen.