Useful Snippets

A collection of useful code snippets. Here you can find code that allows you to get to get started on common tasks in Mesa.

Models with Discrete Time

If you have Multiple type agents and one of them has time attribute you can still build a model that is run by discrete time. In this example, each step of the model, and the agents have a time attribute that is equal to the discrete time to run its own step.

if self.model.schedule.time in self.discrete_time:
    self.model.space.move_agent(self, new_pos)

Implementing Model Level Functions in Staged Activation

In staged activation, if you may want a function to be implemented only on the model level and not at the level of agents. For such functions, include the prefix “model.” before the model function name, when defining the function list. For example, consider a central employment exchange which adjust the wage rate common to all laborers in the direction of excess demand.

Using `numpy.random`

Sometimes you need to use numpy’s random library, for example to get a Poisson distribution.

class MyModel(Model):
    def __init__(self, ...):
        super().__init__()
        self.random = np.random.default_rng(seed)

And just use numpy’s random as usual, e.g. self.random.poisson().

Using multi-process `batch_run` on Windows

You will have an issue with batch_run and number_processes = None. Your cell will show no progress, and in your terminal you will receive AttributeError: Can’t get attribute ‘MoneyModel’ on <module ‘__main__’ (built-in)>. One way to overcome this is to take your code outside of Jupyter and adjust the above code as follows.

from multiprocessing import freeze_support

params = {"width": 10, "height": 10, "N": range(10, 500, 10)}

if __name__ == '__main__':
    freeze_support()
    results = batch_run(
            MoneyModel,
            parameters=params,
            iterations=5,
            max_steps=100,
            number_processes=None,
            data_collection_period=1,
            display_progress=True,
    )

If you would still like to run your code in Jupyter you will need to adjust the cell as noted above. Then you can you can add the nbmultitask library or look at this stackoverflow.