Every variable is defined for a type of entity: for instance persons or households.

However, I may for instance:

  • in a formula defined for a person, want to know some property of their household.

  • in a formula defined for a household, want to know some property of the household members.

Group entity composition

You can get the number of person with a given role in an entity with the nb_persons(role) method. If no role is given, it will return the numbers of people in the entity.

    def formula(household, period):
        nb_persons = household.nb_persons()
        nb_adults = household.nb_persons(Household.ADULT)
        nb_children = household.nb_persons(Household.CHILD)

Note that roles are constants that can be accessed from their entity with the notation Entity.ROLE (in uppercase).

Check if a person has a given role

You can know whether a person has a certain role with the has_role(role) method:

    def formula(person, period):
        is_adult = person.has_role(Household.ADULT)
        is_child = person.has_role(Household.CHILD)


For an entity, several methods allow you to aggregate the values of a quantity defined for its members.

entity.members('variable_name', period) allows you to calculate the value of a variable for all members of an entity.

entity.sum(result) sums previously calculated results. Similar functions such as min, max, any, and all work the same way.

For instance, let’s imagine a basic income paid to households with the following rules:

  • Any household is entitled to 500€ a month per adult, and 200€ a month per children.

  • The sum of salaries from all household members are deducted from the amount of the benefit.

class basic_income(Variable):
    value_type = float
    entity = Household
    label = u"Basic income paid to households"
    definition_period = MONTH

    def formula(household, period):
        nb_adults = household.nb_persons(Household.ADULT)
        nb_children = household.nb_persons(Household.CHILD)
        salaries = household.members('salary', period)
        sum_salaries = household.sum(salaries)

        result = nb_adults * 500 + nb_children * 200 - sum_salaries
        result = max_(result, 0)

        return result


person.entity('variable_name', period) allows you to get the value of variable_name for the entity containing person.

Let’s for example consider that any college student whose family benefits from the basic income will also individually be granted a scholarship of 100€ per month:

class college_scholarship(Variable):
    value_type = float
    entity = Person
    label = u"College Scholarship for basic income recipients."
    definition_period = MONTH

    def formula(person, period):
        is_student = person('is_student', period)
        has_household_basic_income = person.household('basic_income', period) > 0

        return is_student * has_household_basic_income * 100

Similarly, entity.unique_role('variable_name', period) allows you to get the value of variable_name for person who has the role unique_role in entity.

For instance, let’s assume Household has two unique roles, main_declarant and partner.

def formula(household, period):
    household.main_declarant('salary', period) # main declarant's salary
    household.partner('salary', period) # partner's salary