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Bugfix for pickling dynamically modified grids#3217

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quaquel merged 4 commits intomesa:mainfrom
quaquel:grid_pickle
Jan 28, 2026
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Bugfix for pickling dynamically modified grids#3217
quaquel merged 4 commits intomesa:mainfrom
quaquel:grid_pickle

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@quaquel quaquel commented Jan 27, 2026 •
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This bugfix updates Cell.__getstate__ and Grid.__setstate__ to ensure that the actual structure of the grid is properly preserved when pickling a grid.

closes #3215

@quaquel quaquel added the bug Release notes label label Jan 27, 2026
EwoutH
EwoutH approved these changes Jan 27, 2026
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Thanks.

Since pickling has been more often an issue (#2378, #3086, and most recently #3205), should we create a follow-up issue to increase test coverage on pickling follow-up? And maybe pickle and unpickle our example models in a test?

mesa/discrete_space/discrete_space.py Outdated
for cell in self._cells.values():
connections = {
coordinate: self._cells[coordinate]
for coordinate in cell.connections.keys()
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@EwoutH EwoutH Jan 27, 2026 •
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To fix ruff / pre-commit

Suggested change
for coordinate in cell.connections.keys()
for coordinate in cell.connections

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@quaquel quaquel Jan 27, 2026

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Grid pickling was covered by tests, but not for dynamically modified grids. Theoretically, the grid data structure allows for dynamic modifications. However, because of the caching, which is essential for performance, we did not develop that further into a real API. #3086 was just taking advantage of a version bump on the minimum Python side, so not a bug.

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ShreyasN707 commented Jan 27, 2026

Thanks.

Since pickling has been more often an issue (#2378, #3086, and most recently #3205), should we create a follow-up issue to increase test coverage on pickling follow-up? And maybe pickle and unpickle our example models in a test?

@quaquel Thanks for jumping on this so quickly — it’s great to see this getting fixed. I’d be happy to help add some tests around pickling/unpickling dynamic grids or example models if that would be useful.

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github-actions bot commented Jan 27, 2026

Performance benchmarks:

Model Size Init time [95% CI] Run time [95% CI]
BoltzmannWealth small 🔵 -3.8% [-4.5%, -2.9%] 🔵 -2.1% [-2.3%, -1.8%]
BoltzmannWealth large 🔵 -0.3% [-1.1%, +0.6%] 🔵 -0.7% [-3.5%, +2.0%]
Schelling small 🔵 -1.8% [-2.2%, -1.4%] 🔵 -0.9% [-1.1%, -0.6%]
Schelling large 🔵 -0.9% [-1.6%, -0.1%] 🔵 -1.5% [-3.3%, +0.7%]
WolfSheep small 🔵 -2.5% [-2.9%, -2.1%] 🔵 -0.9% [-1.1%, -0.7%]
WolfSheep large 🔵 -1.7% [-3.3%, -0.2%] 🔵 -2.4% [-4.8%, -0.2%]
BoidFlockers small 🔵 -2.7% [-3.1%, -2.4%] 🔵 +1.7% [+1.5%, +2.0%]
BoidFlockers large 🔵 -3.0% [-3.4%, -2.4%] 🔵 +1.1% [+1.0%, +1.3%]

@quaquel quaquel merged commit 105c0d0 into mesa:main Jan 28, 2026
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@quaquel quaquel deleted the grid_pickle branch February 4, 2026 19:37
@EwoutH EwoutH changed the title Bugfix for pickling dynamicly modified grids Bugfix for pickling dynamically modified grids Feb 11, 2026
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Grid connectivity changes are lost after pickle / unpickle

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@quaquel @ShreyasN707 @EwoutH