fix: migrate codebase to Mesa 4.x API (resolves mesa.space removal) by abhinavk0220 · Pull Request #153 · mesa/mesa-llm

abhinavk0220 · 2026-03-05T17:26:37Z

Closes #152

Summary

Mesa 4.x removed mesa.space entirely. This PR migrates the full codebase to the new Mesa 4.x APIs so that mesa-llm works with the current version of Mesa.

Changes

Replace MultiGrid/SingleGrid with OrthogonalMooreGrid from mesa.discrete_space
Replace old ContinuousSpace(x_max, y_max) with new dimensions-based API
Fix agent placement to use cell-based API (agent.cell = grid._cells[pos])
Fix neighbor lookup using get_neighborhood() + coordinate set matching
Fix model.steps → model.step (renamed in Mesa 4.x)
Fix Model.__init__(seed=...) kwarg incompatibility with mesa_signals

Testing

All 203 tests passing after migration:

Notes

Tested against Mesa 4.x dev installed from source.

GSoC contributor checklist

Context & motivation

Mesa 4.x removed mesa.space entirely with no deprecation warning
any project depending on it simply breaks at import time. I discovered
this while trying to run mesa-llm examples and getting immediate
ImportError. This PR is the full migration of the codebase to the
new Mesa 4.x spatial API.

What I learned

Mesa 4.x's new discrete space architecture is fundamentally different
from the old API not just renamed imports but a completely different
cell-based model where agents live in cells rather than coordinates.
Understanding this required reading Mesa's source code directly, not
just the migration guide. The most subtle change was the coordinate
convention difference between OrthogonalMooreGrid._cells (x,y) and
the internal connections dict (row,col) a distinction that caused
agents to move in the wrong direction and required a separate fix in
PR #195.

Learning repo

🔗 My learning repo: https://github.com/abhinavk0220/GSoC-learning-space
🔗 Relevant model(s): https://github.com/abhinavk0220/GSoC-learning-space/tree/main/models

Readiness checks

This PR addresses an agreed-upon problem (linked issue or discussion with maintainer approval), or is a small/trivial fix
I have read the contributing guide and deprecation policy
I have performed a self-review: I reviewed my own PR as if I were a reviewer and left comments on anything that needs explanation
Another GSoC contributor has reviewed this PR:
Tests pass locally (`pytest --cov=mesa tests/)
Code is formatted (ruff check . --fix)
If applicable: documentation, examples, and/or migration guide are updated

…rely, breaking the full test suite.This commit migrates all affected files to the new APIs.Changes:- Replace MultiGrid/SingleGrid imports with OrthogonalMooreGrid from mesa.discrete_space- Replace old ContinuousSpace(x_max, y_max) with new dimensions-based API- Fix agent placement to use cell-based API (agent.cell = grid._cells[pos])- Fix neighbor lookup using get_neighborhood + coordinate set matching- Fix model.steps -> model.step (renamed in Mesa 4.x)- Remove seed= kwarg from Model.__init__ calls (mesa_signals compat fix)- Fix record_model.py self.steps -> self.stepAll 203 tests now passing.

coderabbitai · 2026-03-05T17:26:51Z

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…ools.py to use Mesa 4.x cell-based API- Replace place_agent() with agent.cell = grid._cells[pos]- Fix ContinuousSpace boundary/torus tests for new API behavior- Remove SingleGrid|MultiGrid references from inbuilt_tools.py- All 262 tests passing

for more information, see https://pre-commit.ci

…Schelling's (1971) classic segregation model using LLM agentsinstead of a fixed tolerance threshold.Each agent reasons in natural language about its neighborhood compositionand decides whether to stay ('happy') or relocate ('unhappy'). Thisproduces richer segregation dynamics than the classical threshold rule.Includes:- SchellingAgent extending LLMAgent with CoT reasoning- LLMSchellingModel on OrthogonalMooreGrid with torus=True- Segregation index metric tracked over time- SolaraViz with grid plot, happiness chart, and segregation index- README with comparison table vs classical Schelling modelReference: Schelling, T.C. (1971). Dynamic models of segregation.Journal of Mathematical Sociology, 1(2), 143-186.Related: mesa/mesa-llm#153

Jay-Lokhande · 2026-03-09T16:26:53Z

Hey this looks cool,
actually i have cloned your branch but not getting how did you tested against Mesa 4.x would please help me out for this?

colinfrisch · 2026-03-10T09:17:04Z

I'm not fully up to date with the latest mesa 4.x changes... @wang-boyu what do you think about this ?

abhinavk0220 · 2026-03-10T10:37:21Z

Hey Jay! To test against Mesa 4.x, install Mesa directly from
source:

git clone https://github.com/mesa/mesa.git
cd mesa
pip install -e .

Then install mesa-llm dependencies:

cd ../mesa-llm
pip install -e .

Then run the test suite:

python -m pytest tests/ -q

The key Mesa 4.x changes that affect mesa-llm are:

mesa.space is removed → use mesa.discrete_space and
mesa.experimental.continuous_space
Model(seed=42) constructor changed
model._time replaces model.steps as step counter

Happy to help if you run into issues! 🙂

abhinavk0220 · 2026-03-10T10:37:42Z

Hi Colin! Happy to provide more context for wang-boyu's review.

The key Mesa 4.x breaking changes this PR addresses:

mesa.space removed entirely → migrated to mesa.discrete_space
(OrthogonalMooreGrid) and mesa.experimental.continuous_space
ContinuousSpace API changed → old positional args replaced
with dimensions=[[0,x],[0,y]] keyword API
model.steps → model._time as the internal step counter
Model(seed=42) constructor incompatibility with mesa_signals

All 203 tests passing after migration. Happy to answer any
specific questions wang-boyu has!

Jay-Lokhande · 2026-03-14T07:32:31Z

I was trying to understand changes you made I am not getting that 'hell' named file you have created or might generated.

abhinavk0220 · 2026-03-14T18:37:31Z

mesa_llm/tools/inbuilt_tools.py

    OrthogonalMooreGrid,
    OrthogonalVonNeumannGrid,
 )
-from mesa.space import (


Replaced mesa.space imports with mesa.discrete_space and
mesa.experimental.continuous_space throughout. The ContinuousSpace
API also changed old positional args (x_max, y_max) replaced with
dimensions=[[0,x],[0,y]] keyword API. Agent placement migrated from
grid.place_agent() to cell-based API: cell.add_agent(agent) +
agent.cell = cell.

AdityaChauhanX07 · 2026-03-14T20:46:10Z

A few things worth noting for the review:

This was tested against Mesa 4.x from source, not the official pre-release (pip install --pre mesa). Worth verifying against the pre-release since that's what most users will actually install.
There are merge conflicts that will need resolving before this lands.

abhinavKumar0206 and others added 5 commits March 6, 2026 08:40

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fix: resolve ruff linting errors (PLC0415, F841)

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fix: move import math to top level (ruff PLC0415)

951a5c4

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abhinavk0220 mentioned this pull request Mar 6, 2026

feat: add LLM Opinion Dynamics example using mesa-llm mesa/mesa-examples#360

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This was referenced Mar 6, 2026

feat: add LLM Schelling Segregation example using mesa-llm mesa/mesa-examples#363

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improve: add comprehensive type hints to LLMAgent and ModuleLLM #170

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improve: add type hints to reasoning module + fix Mesa 4.x compatibility #179

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colinfrisch assigned wang-boyu Mar 10, 2026

abhinavk0220 commented Mar 14, 2026

View reviewed changes

abhinavk0220 mentioned this pull request Mar 17, 2026

Add __repr__ methods to core classes and fix Mesa 4.x API compatibility #195

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fix: migrate codebase to Mesa 4.x API (resolves mesa.space removal)#153

fix: migrate codebase to Mesa 4.x API (resolves mesa.space removal)#153
abhinavk0220 wants to merge 6 commits intomesa:mainfrom
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Summary

Changes

Testing

Notes

GSoC contributor checklist

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What I learned

Learning repo

Readiness checks

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