Add example LangChain app. Add Jupyter. Add container dependencies for GraphViz. (#3)

Author: briangershon

Dockerfile

@@ -7,9 +7,18 @@ ENV PYTHONDONTWRITEBYTECODE=1
 # Turns off buffering for easier container logging
 ENV PYTHONUNBUFFERED=1
 
-# install git
+# install system dependencies
 RUN apt-get update && apt-get install -y \
-    git gnupg2 \
+    git \
+    gnupg2 \
+    python3-dev \
+    graphviz \
+    graphviz-dev \
+    pkg-config \
+    gcc \
+    libcairo2-dev \
+    libpango1.0-dev \
+    libgdk-pixbuf2.0-dev \
     && rm -rf /var/lib/apt/lists/*
 
 # Install pip requirements

README.md

@@ -2,11 +2,11 @@
 
 Use a VSCode dev container as your virtual Python development environment.
 
-## Features
+Includes dependencies for LangChain, LangGraph, Juypter Notebook, and PyGraphviz (for visualization).
 
-- Dockerized development environment and VSCode devcontainer setup
-- Use `pip` to install Python packages
-- Set environment variables in `.env` file
+Example LangChain and LangGraph code.
+
+Load environment variables via `.env` file.
 
 ## Getting Started
 
@@ -34,3 +34,11 @@ Open up a terminal in VSCode.
 Run `env` to verify env vars look good.
 
 `python app.py`
+
+## Running a Jupyter Notebook
+
+In VSCode terminal, run `jupyter notebook --allow-root`. Open up a browser and navigate to the URL shown in terminal. `--allow-root` is fine since Python is running in a dev container.
+
+In browser UI, create a new Python 3 notebook to get started.
+
+If you copy in `app.py` into the notebook, you can run the code in the notebook and also see graphviz visualizations of the workflow.

app.py

@@ -1,9 +1,86 @@
+from typing import TypedDict
+
+from IPython.display import Image, display
 from langchain.prompts import ChatPromptTemplate
 from langchain_openai import ChatOpenAI
+from langgraph.graph import END, StateGraph
+
+# EXAMPLE LANGCHAIN
+print("Example: Create a haiku with LangChain:\n\n")
 
 llm = ChatOpenAI(temperature=0.9, model="gpt-4o-mini")
 prompt = ChatPromptTemplate.from_template("Create a haiku from:\n\n{content}")
 chain = prompt | llm
 
 response = chain.invoke({"content": "The quick brown fox jumps over the lazy dog."})
 print(response.content)
+
+# EXAMPLE LANGGRAPH
+print(
+    "\n\nExample: Determine if prompt is discussing colors or not with LangGraph:\n\n"
+)
+
+
+# Define the state of our graph
+class State(TypedDict):
+    prompt: str
+    is_color: bool
+    result: str
+
+
+# Define our nodes
+def ask_for_prompt(state: State) -> State:
+    prompt = input("Please enter a prompt to indentify if it mentions a color or not: ")
+    return {"prompt": prompt, "is_color": False, "result": ""}
+
+
+def evaluate_prompt(state: State) -> State:
+    prompt = state["prompt"]
+    is_color = False
+
+    llm = ChatOpenAI()
+    prompt = ChatPromptTemplate.from_template(
+        "Evaluate if this prompt discusses colors: '{prompt}'. Respond with 'Yes' or 'No'."
+    )
+    response = llm.invoke(prompt.format_prompt(prompt=state["prompt"]))
+    if isinstance(response.content, str):
+        is_color = response.content.strip().lower() == "yes"
+    return {**state, "is_color": is_color}
+
+
+def show_result(state: State) -> State:
+    if state["is_color"]:
+        result = f"The prompt '{state['prompt']}' contains a color!"
+    else:
+        result = f"The prompt '{state['prompt']}' does not contain a color."
+    print(result)
+    return {**state, "result": result}
+
+
+# Create the graph
+workflow = StateGraph(State)
+
+# Add nodes
+workflow.add_node("ask_prompt", ask_for_prompt)
+workflow.add_node("evaluate", evaluate_prompt)
+workflow.add_node("show_result", show_result)
+
+# Add edges
+workflow.add_edge("ask_prompt", "evaluate")
+workflow.add_edge("evaluate", "show_result")
+workflow.add_edge("show_result", END)
+
+# Set entry point
+workflow.set_entry_point("ask_prompt")
+
+# Compile the graph
+app = workflow.compile()
+
+display(Image(app.get_graph().draw_png()))  # type: ignore
+
+# Run the graph
+for output in app.stream({"prompt": "", "is_color": False, "result": ""}):
+    pass
+
+# Example usage:
+# This will run until a color is mentioned in the prompt

requirements.txt

@@ -1,4 +1,8 @@
 langchain==0.2.14
 langchain-openai==0.1.22
 langchain-community==0.2.12
+langgraph==0.2.16
 faiss-cpu==1.8.0.post1
+jupyter==1.1.1
+pygraphviz==1.13
+