Running Models

Introduction

This is the fourth tutorial in the Intro Series where we do a deeper dive into running models built using the Footings framework.

Running Models

We will start with the code from the prior tutorial.

from footings.model import (
    model,
    step,
    def_parameter,
    def_intermediate,
    def_return,
)

@model(steps=["_add_a_b", "_add_ab_c"])
class AddABC:
    """This model takes 3 parameters - a, b, and c and adds them together in two steps."""
    a = def_parameter(dtype=int, description="This is parameter a.")
    b = def_parameter(dtype=int, description="This is parameter b.")
    c = def_parameter(dtype=int, description="This is parameter c.")
    ab = def_intermediate(dtype=int, description="This holds a + b.")
    abc = def_return(dtype=int, description="The sum of ab and c.")

    @step(uses=["a", "b"], impacts=["ab"])
    def _add_a_b(self):
        """Add a and b together and assign to ab."""
        self.ab = self.a + self.b

    @step(uses=["ab", "c"], impacts=["abc"])
    def _add_ab_c(self):
        """Add ab and c together for final return."""
        self.abc = self.ab + self.c

As shown in the first tutorial, we can call the run method to run the model.

AddABC(a=1, b=2, c=3).run()

6

The run method does take one optional argument to_step which you can pass the step to which you want to run the model too. This can be useful for debugging purposes.

to_ab = AddABC(a=1, b=2, c=3).run(to_step="_add_a_b")
print(f"AddABC.ab  = {str(to_ab.ab)}")
print(f"AddABC.abc = {str(to_ab.abc)}")

AddABC.ab  = 3
AddABC.abc = None

As the code above shows, running the model to step _add_a_b assigns the ab the value 3 but leaves abc None because it is not touched until the next step.

Models with Multiple Return Attributes

If a model has multiple return attributes, the model will return a tuple of the attributes. This is demonstrated below. Note we changed the attribute ab from using def_intermediate to def_return.

@model(steps=["_add_a_b", "_add_ab_c"])
class AddABC:
    """This model takes 3 parameters - a, b, and c and adds them together in two steps."""
    a = def_parameter(dtype=int, description="This is parameter a.")
    b = def_parameter(dtype=int, description="This is parameter b.")
    c = def_parameter(dtype=int, description="This is parameter c.")
    ab = def_return(dtype=int, description="This holds a + b.")
    abc = def_return(dtype=int, description="The sum of ab and c.")

    @step(uses=["a", "b"], impacts=["ab"])
    def _add_a_b(self):
        """Add a and b together and assign to ab."""
        self.ab = self.a + self.b

    @step(uses=["ab", "c"], impacts=["abc"])
    def _add_ab_c(self):
        """Add ab and c together for final return."""
        self.abc = self.ab + self.c

AddABC(a=1, b=2, c=3).run()

(3, 6)

Do note that the return attributes are returned in order of declaration within the model.

Closing

With this tutorial, we dug a little deeper into running models and the possibility of returning multiple attributes upon execution of a model. In the next tutorial, we will look at how we can audit models and see what each step does as the model runs.

Documenting Models Auditing Models