Python Integration with Archer

Archer offers seamless integration with Python, enabling users to incorporate Python scripts into their Archer models directly. This guide provides a detailed explanation of this integration, showcasing its versatility and ease of use.

Including a Python Script

To bring a Python script into your Archer model, utilize the import directive:

model Phone {
  import "filename.py"  // Reference to the Python script

  Phone - mandatory -> Screen
  ...
}

Sample Python Script

Consider the following Python script:

@after_update()
def method_after_update():
  values = fetchValuesFromExternalApi()
  sumOfValues = sum(values)

  assign_property('Feature1.ExternalValues', values)

  add_constraint(lambda: model.Feature2.Value > sumOfValues)

This script highlights the three primary features of Archer's Python integration:

1. Event hooks: Call Python functions at specific points in the configuration's lifecycle.
2. Direct Property Assignment: You can assign values from your Python script directly to variables in your Archer model, using the assign_property method.
3. Constraint Addition: Use the add_constraint function to introduce new constraints.

Accessing and Setting Variable Properties

The Python integration introduces a global model object. Through this, you can interface with Archer model variables.

value = model['VariableName']['Value']

Note: The Selected and Value properties start with uppercase letters.

To assign a value to a model variable's property:

valueCalculatedFromApi = fetchValueFromApi()

assign_property('VariableName.PropertyName', valueCalculatedFromApi)

Python integration supports assignment of intricate object structures, including arrays:

assign_property('VariableName.ComplexObjectPropertyName', {
  'NestedObject': {
    ExampleValue: 123,
    ExampleArray: [1, 2, 3],
    'NestedNestedObject': {
      ObjectValue: True
    }
  }
})

Such complex structures are fully accessible within your Archer model:

model Example {
  Example - mandatory -> VariableName
  Example - optional -> Option1

  // Option1 visibility is contingent upon ObjectValue being true
  condition Option1 = VariableName.NestedObject.NestedNestedObject.ObjectValue

  // Using values from ExampleArray to determine Option1's lower bound value
  forall v in VariableName.NestedObject.ExampleArray {
    lower_bound Option1 = v * 2
  }
}

Incorporating Additional Constraints

Augment your Archer model with constraints defined in Python:

pythonValue = 123

add_constraint(lambda: model['Variable1']['Value'] >= model['Variable2']['Value'] * pythonValue)

Using the traverse Method

The traverse method facilitates iteration over child variables of a given parent variable:

Given this Archer model:

model Example {
  Example - mandatory -> Group
  Group - optional -> Option1
  Group - optional -> Option2
  Group - optional -> Option3
}

You can loop over all of Group's options:

for c in traverse(model['Group']):
  add_constraint(lambda: c.Value > 10)

Available hooks:

Name	Decorator	Description
Before update	@before_update	Invoked before a user requirement is updated in the solver.
After update	@after_update	Invoked after a user requirement is updated in the solver.