Order Book Project

Created by Anjali and Finnley

An educational Streamlit application for adding buy and sell orders, viewing bids and asks, and removing an order when it is purchased or sold into.

This demonstrates order-book concepts. It is not connected to an exchange and must not be used for real trading.

Preview

Features

• Add buy and sell orders with a symbol, quantity, and total price.
• Display bids and asks in separate columns.
• Sort buy orders from highest to lowest price.
• Sort sell orders from lowest to highest price.
• Assign matching colours to orders at the same price.
• Purchase a selected sell order.
• Sell into a selected buy order.
• Remove the oldest matching order when duplicates exist.
• Validate empty, numeric, and negative inputs.

Run locally

python -m pip install -r requirements.txt
streamlit run main.py

Streamlit normally opens the application in a browser. If it does not, use the local URL printed in the terminal.

How the order book works

Add an order

1. Choose Add Stock Order.
2. Select Buy or Sell.
3. Enter a stock symbol, quantity, and total price.
4. Submit the form.

The application uppercases the symbol, generates a six-digit order ID, records the current time, and assigns a colour based on the price.

Complete an order

Choose Purchase Sell Order or Sell to Buy Order, then select a symbol and one of its displayed price and quantity combinations.

The app removes one complete matching order. It does not support partial fills.

Current data behaviour

The order book is stored in Streamlit session state:

• Refreshing or restarting the session can reset the data.
• There is no database or file persistence.
• New sessions begin with demonstration orders already present in main.py.
• The app does not match compatible orders automatically.
• Prices are stored as entered strings and converted when sorting.

Display rules

Side	Sort order	Market term
Buy	Highest price first	Bid
Sell	Lowest price first	Ask

Orders with the same price share a colour. When several orders have the same symbol, price, and quantity, the oldest one is removed first.

Project files

• main.py, complete Streamlit interface and in-memory order book.
• requirements.txt, pinned Python environment.
• help.txt, short launch reminder.
• .vscode/settings.json, editor configuration.

What this demonstrates

The project combines a stateful Streamlit interface with validation, sorted bid and ask views, price-based colour grouping, and first-in handling for duplicate orders. It was built as a collaborative learning project, so the README keeps the original attribution while documenting the current limitations clearly.

Possible improvements

• Replace the demonstration data with an empty initial book option.
• Add persistent storage.
• Support partial fills and remaining quantities.
• Add automatic price matching.
• Separate the matching logic from the Streamlit interface.
• Add automated tests for validation and order priority.

Licence

No project-level licence is currently included.