[Bug Report] pymunk>7.0.0 breaks the waterworld env

[JiangpengLI86]

Dependency Version Constraint Allows Breaking Changes in pymunk

The current project dependency specification only constrains pymunk to versions greater than 6.2.0:

PettingZoo/pyproject.toml

Line 43 in 9c1c5f1

sisl = ["pygame>=2.3.0", "pymunk>=6.2.0", "box2d-py>=2.3.5", "scipy>=1.4.1"]

PettingZoo/pyproject.toml

Line 60 in 9c1c5f1

"pymunk>=6.2.0",

However, according to the official pymunk changelog, version 7.0.0 introduces a significant breaking change to the CollisionHandler API:

https://www.pymunk.org/en/latest/changelog.html#pymunk-7-0-0-2025-05-28

As a result, existing code paths that rely on the pre-7.0.0 CollisionHandler behavior will fail when a newer pymunk version is installed. For example, the following usage is no longer compatible:

PettingZoo/pettingzoo/sisl/waterworld/waterworld_base.py

Line 321 in 9c1c5f1

self.space.add_collision_handler(

Specifically, calls such as self.space.add_collision_handler(...) break under pymunk ≥ 7.0.0.

Code example

from pettingzoo.sisl import waterworld_v4
env = waterworld_v4.parallel_env()
env.reset()

System info

PettingZoo version: 1.25.0
Ubuntu 2204
Python 3.12.9

Suggested Resolution

• Add an explicit upper bound on the pymunk dependency (e.g., <7.0.0), or
• Update the affected code to be compatible with pymunk ≥ 7.0.0

Checklist

• I have checked that there is no similar issue in the repo

[dm-ackerman]

hmmm, I remember fixing this by updating the env while on a flight a while back. I guess it never made it into main. I'll look for those changes and see if i can submit a pull request if the issue is still pending when i find them.

Until it gets fixed, a simple work around is to run pip install pymunk==6.11.1 after installing pettingzoo to downgrade the pymunk version.

[JiangpengLI86]

Yup. Installing a fixed version with pip install pymunk==6.11.1 resolves the issue.

Thank you for the prompt response. Please feel free to close this issue after the corresponding PR.