A pure Python implementation of the Cassowary constraint-solving algorithm. Cassowary is the algorithm that forms the core of the OS X and iOS visual layout mechanism.


Cassowary is compatible with both Python 2 or Python 3. To install Cassowary in your virtualenv, run:

$ pip install cassowary

Then, in your Python code, you can create and solve constraint systems. See the documentation for examples of what this looks like in practice.


Notice: Cassowary is no longer part of the BeeWare suite.
You can talk to the community through:


If you experience problems with Cassowary, log them on GitHub. If you want to contribute code, please fork the code and submit a pull request.

Project Administration

This project was transferred to Brodderick Rodriguez in February 2020. He will continue to oversee its development from here on out.
Russell Keith-Magee is the original author of this work (2013 - 2019). A big thanks to him for his work! Check out Russell’s GitHub.

Indices and tables