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new feature: AgentSet.get can retrieve one or more then one attribute #2044

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merged 7 commits into from
Feb 21, 2024
Merged

new feature: AgentSet.get can retrieve one or more then one attribute #2044

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a510b34
new feature: AgentSet.get can retrieve one or more then one attribute
quaquel Feb 20, 2024
cb78523
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Feb 20, 2024
22cd104
minor docstring update
quaquel Feb 20, 2024
5f96227
[pre-commit.ci] auto fixes from pre-commit.com hooks
pre-commit-ci[bot] Feb 20, 2024
76bb633
add AttributeError to docstring and fixes capital L in List
quaquel Feb 21, 2024
c0660a4
Update agent.py
quaquel Feb 21, 2024
c441910
Update agent.py
quaquel Feb 21, 2024
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19 changes: 13 additions & 6 deletions mesa/agent.py
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Original file line number Diff line number Diff line change
Expand Up @@ -17,7 +17,7 @@
from random import Random

# mypy
from typing import TYPE_CHECKING, Any, Callable
from typing import TYPE_CHECKING, Any, Callable, List

if TYPE_CHECKING:
# We ensure that these are not imported during runtime to prevent cyclic
Expand Down Expand Up @@ -264,17 +264,24 @@ def do(

return res if return_results else self

def get(self, attr_name: str) -> list[Any]:
def get(self, attr_names: str | list[str]) -> list[Any]:
"""
Retrieve a specified attribute from each agent in the AgentSet.
Retrieve the specified attribute(s) from each agent in the AgentSet.

Args:
attr_name (str): The name of the attribute to retrieve from each agent.
attr_names (str | List[str]): The name(s) of the attribute(s) to retrieve from each agent.
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The List here shouldn't be capitalized.

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The return value also has a capitalized List. This may be a small typo, but it can't be automatically fixed by pyupgrade.


Returns:
list[Any]: A list of attribute values from each agent in the set.
list[Any]: A list of attribute values for each agent in the set.
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Is this still correct? Would it be nested in some sort when a list of attrs is inputted?

Maybe make a little bit more explicit what is returned when a str is inputted for attr_names, and what when a list of strings is inputted.

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see the updated text

"""
return [getattr(agent, attr_name) for agent in self._agents]

if isinstance(attr_names, str):
return [getattr(agent, attr_names) for agent in self._agents]
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Maybe we should default to None (getattr(agent, attr_names, None)). This way it would be easier to collect across different agent types, which might or might not have the specified attributes.

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I see your point but I am torn. I personally probably would prefer getting the error explicitly rather than being confronted with None values downstream.

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Past discussion: projectmesa/mesa-examples#90. The summary is that it depends on the coder's background: in JavaScript, it is not surprising for obj.attr to return undefined and not raise an error. However, Python doesn't distinguish between null and undefined, and so there is an information loss when returning None. It is ambiguous and could mean the modeler intentionally chooses to return None instead of an absence of attribute.
I prefer no fallback to None.

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Maybe we could add a boolean switch (something like allow_undefined) that defaults to False. When False it isn't allowed and an error is returned, when True it is allowed and None values are returned.

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that would make the code internally more complicated. You would get two additional nested if/else.

The easier solution is for the user to do agentset.select("condition to ensure attribute exists").get().

Also, why allow None in the first place? It only gives more downstream problems.

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I think its not necesarily an "error" if we collect None instead of triggering an AttributeError. It depends on the use case. If you quickly want to get some attributes on all of your agents, but some agents don't have that attribute you still get some result. Otherwise you first have to pre-select the right AgentSet and then collect the attributes.

I think the cleanest solution would probably be to mimic getattr in that users can provide a default value for agentset.get() and pass that to getattr, if set.

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implementation wise this is a bit tricky. default in getattr is not a keyword argument but an argument. So you cannot use None to signal you don't specify default.

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We can defer this discussion and implementation in a separate PR. The current behavior in this PR is consistent with the existing API, which does not fall back to undefined/None.

else:
return [
[getattr(agent, attr_name) for attr_name in attr_names]
for agent in self._agents
]

def __getitem__(self, item: int | slice) -> Agent:
"""
Expand Down
18 changes: 18 additions & 0 deletions tests/test_agent.py
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Expand Up @@ -221,6 +221,24 @@ def test_agentset_get_attribute():
with pytest.raises(AttributeError):
agentset.get("non_existing_attribute")

model = Model()
agents = []
for i in range(10):
agent = TestAgent(model.next_id(), model)
agent.i = i**2
agents.append(agent)
agentset = AgentSet(agents, model)

values = agentset.get(["unique_id", "i"])

for value, agent in zip(values, agents):
(
unique_id,
i,
) = value
assert agent.unique_id == unique_id
assert agent.i == i


class OtherAgentType(Agent):
def get_unique_identifier(self):
Expand Down