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check whether model reporter is a partial function#3220

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quaquel merged 1 commit intomesa:mainfrom
wang-boyu:fix/model-reporter-partial-function
Jan 29, 2026
Merged

check whether model reporter is a partial function#3220
quaquel merged 1 commit intomesa:mainfrom
wang-boyu:fix/model-reporter-partial-function

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@wang-boyu wang-boyu commented Jan 29, 2026 •
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fixes #1871

If we use a partial function as a data collector, for example

from functools import partial


def count_agents(model, multiplier):
    return len(model.agents) * multiplier

dc = DataCollector(
    model_reporters={"AgentsTimesTwo": partial(count_agents, multiplier=2)}
)
dc.collect(model)

then we will get a RuntimeError:

# Type 2: Method of class/instance (bound methods are callable)
if callable(reporter) and not isinstance(reporter, types.LambdaType):
    try:
>        reporter()  # Call without args for bound methods
          ^^^^^^^^^^
E               TypeError: TestPartialReporterValidation.test_partial_model_reporter.<locals>.count_agents() missing 1 required positional argument: 'model'

mesa/datacollection.py:172: TypeError

A similar problem was previously fixed in #1872 by checking whether the reporter is a partial function:

# Check if lambda or partial function
if isinstance(reporter, (types.LambdaType, partial)):
    self.model_vars[var].append(reporter(model))

However in #2605 where we extracted a separate function to validate reporters, this check was not performed:

# Type 1: Lambda function
if isinstance(reporter, types.LambdaType):
    ...

This PR essentially added this check into the model reporter validation function:

# Type 1: Lambda function or partial
if isinstance(reporter, (types.LambdaType, partial)):
    ...

and added a test case for when a model reporter is a partial function.

@wang-boyu wang-boyu added the bug Release notes label label Jan 29, 2026
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github-actions bot commented Jan 29, 2026

Performance benchmarks:

Model Size Init time [95% CI] Run time [95% CI]
BoltzmannWealth small 🟢 -5.8% [-6.1%, -5.6%] 🔵 -1.3% [-1.5%, -1.0%]
BoltzmannWealth large 🔵 -1.9% [-2.5%, -1.4%] 🔵 -2.3% [-2.7%, -1.8%]
Schelling small 🔵 -1.3% [-1.5%, -1.0%] 🔵 +0.0% [-0.1%, +0.2%]
Schelling large 🔵 -0.6% [-1.2%, +0.0%] 🔵 +2.4% [+1.4%, +3.2%]
WolfSheep small 🔵 -1.8% [-2.1%, -1.5%] 🔵 +0.6% [+0.4%, +0.7%]
WolfSheep large 🔵 -0.6% [-0.8%, -0.2%] 🔵 +0.4% [+0.0%, +0.7%]
BoidFlockers small 🔵 +1.0% [+0.8%, +1.3%] 🔵 +0.1% [-0.0%, +0.3%]
BoidFlockers large 🔵 +1.5% [+1.1%, +1.9%] 🔵 -0.2% [-0.3%, -0.1%]

@quaquel
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quaquel commented Jan 29, 2026

Can you ensure the starting post is independently readable instead of only a link? Otherwise, this looks fine to me.

@wang-boyu
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wang-boyu commented Jan 29, 2026

Sorry about the trouble. I've edited the description.

@quaquel quaquel merged commit 0944797 into mesa:main Jan 29, 2026
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@wang-boyu wang-boyu deleted the fix/model-reporter-partial-function branch January 29, 2026 14:41
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TyperError when model reporter is a partial function

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@wang-boyu @quaquel