Model: Replace get_agents_of_type method with agents_by_type property

[EwoutH]

This PR replaces the Model method get_agents_of_type() with an agents_by_type property, which directly returns the dict.

Instead of using:

model.get_agents_of_type(Sheep)

You should now use:

model.agents_by_type[Sheep]

Since we also use agents and not get_agents, it's more intuitive to directly have access to the object itself (in this case the agents_by_type dict). It's also is more concise and since you have full dict access, more flexible.

Examples and tests are updated and an deprecation warning is added for get_agents_of_type(). Example models are updated in:

• Replace get_agents_of_type method with agents_by_type property mesa-examples#190

[github-actions]

Performance benchmarks:

Model	Size	Init time [95% CI]	Run time [95% CI]
BoltzmannWealth	small	🔵 -0.6% [-1.9%, +0.6%]	🔵 -0.6% [-0.8%, -0.5%]
BoltzmannWealth	large	🔵 -0.9% [-32.3%, +35.8%]	🔵 -0.7% [-2.9%, +1.5%]
Schelling	small	🔵 +0.1% [-0.3%, +0.4%]	🔵 +1.4% [+1.0%, +1.7%]
Schelling	large	🔵 +0.6% [-0.4%, +1.4%]	🔵 +3.5% [+2.1%, +4.9%]
WolfSheep	small	🔵 -2.0% [-3.1%, -0.8%]	🔵 -2.5% [-2.9%, -2.2%]
WolfSheep	large	🔵 -1.7% [-2.2%, -1.1%]	🟢 -6.2% [-7.1%, -5.4%]
BoidFlockers	small	🔵 -1.6% [-2.0%, -1.1%]	🔵 -0.5% [-1.2%, +0.2%]
BoidFlockers	large	🔵 -2.3% [-3.0%, -1.6%]	🔵 -0.9% [-1.9%, +0.1%]

[quaquel]

I am not against making this change, but agents is an attribute while get_agents_of_type is a method. You are thus comparing two different things. What about turning agents_of_type into an attribute as well, so you would do model.agents_of_type[Sheep]. I prefer methods with names that clearly indicate that something is done (hence the use of get).

[EwoutH]

Fair point. At this point we can just expose the agents_by_type dict though a property, right?

[EwoutH]

Implemented as suggested!

[quaquel]

If you add a test for this in test_model, its good to go as far as I am concerned.

[EwoutH]

Tests are added and the PR description and title are updated with some explanation and examples.

Thanks for reviewing!