Sunfish: A Simple Yet Powerful Chess Engine
Introduction
Sunfish is a lightweight yet robust chess engine written in Python that offers a straightforward approach to chess programming. Despite its compact size—only 131 lines of code—Sunfish plays at a competitive level, boasting a rating above 2000 on Lichess. Its simplicity makes it an excellent platform for experimentation, whether you're testing parallel search algorithms, experimenting with evaluation functions, or developing deep learning chess programs.
Playing Against Sunfish
One can easily engage with Sunfish through a "fancy" terminal interface. Players have the flexibility to choose whether they want to play as White or Black, and the engine provides feedback on moves using algebraic notation. This straightforward interface enables users to make moves without needing complex setup, using simple commands like Nf6 or o-o for castling.
For those interested in a graphical interface, Sunfish can also run on platforms like PyChess or Arena, adding an additional layer of convenience and visual engagement.
Features
Sunfish is built around the efficient MTD-bi search algorithm, known for its speed and simplicity. It incorporates classic chess engine techniques and utilizes Python's standard collections and data structures for clarity and effectiveness.
An intriguing aspect of Sunfish is its efficient evaluation system using Piece Square Tables, which adjusts the engine's strategy based on the pieces' positions.
Limitations and Improvements
While Sunfish adheres to all standard chess rules, it lacks the 50-move draw rule. There are several ways to enhance Sunfish's strength, such as modifying the board representation or implementing a more complex knowledge of chess. Users can also consider using PyPy's Just-In-Time interpreter to achieve a significant boost in performance, enhancing Sunfish's capabilities.
Why Sunfish?
The name "Sunfish" is a nod to the Pygmy Sunfish, one of the few fish with a name starting with "Py," reflecting the Python programming language. It also pays homage to renowned engines like Stockfish, retaining the "fish" tradition in chess engine naming.
NNUE Version
Sunfish also has an experimental version using an Efficiently Updatable Neural Network (NNUE). This version enhances positional play, although there is room for improvement in speed and tactics.
Conclusion
Sunfish, with its open-source GNU GPL v3 license, invites developers to fork the project and explore its full potential. Whether you are a chess enthusiast, a developer, or both, Sunfish offers a versatile and educational experience in chess programming.