LangChain

LangChain Example Python Code

Python Scripts Overview

Script Name	Description	Video Link
01_hello_python.py	Hello world print	https://youtu.be/9lkY-pp62II
02_openai_chat_completion.py	OpenAI chat via openai lib	TBD
03_openai_langchain_chat.py	OpenAI chat via LangChain	TBD
04_streamlit_langchain_chat.py	Streamlit UI for OpenAI chat	TBD
05_streamlit_gdp_llm.py	Streamlit: LLM US GDP chart	TBD
11_ollama.py	install and run gemma3:270m on mac	https://www.youtube.com/watch?v=IUGO8-CawGA https://www.youtube.com/watch?v=NFzaVfFn09o

Get the code

You can either create a local folder named LangChain and work there, or clone this repository directly.

Quick start (VS Code, venv, OpenAI key)

1. Open the project folder in VS Code
2. Open Terminal
3. Create a one-time virtual environment using Python 3.11 and activate it:

python3.11 -m venv .venv
source .venv/bin/activate

In the future, re-activate the virtual environment with:

source .venv/bin/activate

After activating the virtual environment, install the project dependencies:

pip install -r requirements.txt

If you don't have Python installed yet, install Homebrew first and then install Python (see the "Install brew on Mac" section below).

4. Make sure you have an OpenAI API key. Then add it to your environment (example):

export OPENAI_API_KEY="sk-proj-w5W..."

Important: issue the above command in the same terminal window where you issues the source command above.

5. Create a simple hello world script 01_hello_python.py:

print("Hello, LangChain!")

Run it with:

python 01_hello_python.py

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Streamlit US GDP Chart Example

To run the Streamlit app that fetches and plots US GDP (last 5 years) using an LLM:

streamlit run 05_streamlit_gdp_llm.py

Install brew on Mac

If you're on macOS, install Homebrew first (Homebrew is the recommended package manager for macOS).

Install Homebrew by running the official installer in a terminal:

/bin/bash -c "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/HEAD/install.sh)"

It will ask you to type sudo password. Make sure to close the Terminal and start a new one.

If you're on Linux or Windows, use your platform's package manager (apt, yum, choco, winget, etc.), or install Homebrew on Linux if you prefer.

Install Python

If you're on macOS you can install Python 3.11 via Homebrew:

brew install python@3.11

Install Ollama

Download Ollama Open Terminal and run ollama list -- to see models already downloaded ollama pull gemma3:270m -- gets the gemma3:270m model ollama run gemma3:270m -- runs the gemma3:270m model ollama ps -- shows the running models ollama stop gemma3:270m -- stops the gemma3:270m model