Input Data

You can use OpenFisca with two kinds of input information:

  • either test cases: you simulate the legislation for one standard situation
  • or data: you provide a population (survey with aggregated data, CSV files with bulk data, etc.) on which you want to apply the legislation


The interface between input information and input variables that OpenFisca can handle is called Scenario.

Technically speaking, OpenFisca is using vector computing for performance reasons via the NumPy Python package

Whatever the input is, test case or data, the scenario converts it into vectors internally.

Application: how to create a scenario

After initializing the Tax and Benefit System, you now want to create a scenario that will allow you in a second step to give input information.

# Create a scenario
scenario = tax_benefit_system.new_scenario()

Test cases

A test case describes persons and entities with their input variables or attributes.

You may add information at the individual level or at the entity level. One input is crucial and shouldn’t be forgotten: the period of the simulation.

Application: how to initialize a scenario

Test cases can be expressed in Python, or in JSON when using the Web API (see the specific section of the documentation).

In Python, you have to use the init_single_entity function based on the scenario. To give to every person of your test case attributes, you have to use the Python dictionary object.

We show here the Python expression for a family constituted by:

  • two parents (with attributes: her age or her date_naissance and her salaire_de_base)
  • two children (with attribute: their age)
  • a house (with attributes: the loyer and the statut_occupation_logement)
# Initialize test case
    period = 2015,
# Variable describing the individuals
    parent1 = dict(
        age = 30,
        salaire_de_base = 15000, # Annual basis
    parent2 = dict(
        date_naissance = date(1980, 1, 1),
        salaire_de_base = 70000, # Annual basis
     enfants = [
        dict(age = 12),
        dict(age = 18),
 # Variable describing the entity
    menage = dict(loyer = 12000, # Annual basis
            statut_occupation_logement = u"Locataire ou sous-locataire
                                      d'un logement loué vide non-HLM",

Notice that some input variables are associated to individus (“parent1” , “parent2” and “children”) whereas other are related to entity (“menage”).

WARNING: Declare the input variables on an annual basis.

HINT: For categorical variables you may use either the modality or its number. Example with the statut d’occupation du logement:

# Declaration of categorical variable
menage = dict(loyer = 12000,
           statut_occupation_logement = 4,


OpenFisca input data can vary from one situation to a whole population. This data could come from a survey with aggregated data, data files extracted from a database, etc.

CSV data

To apply the legislation on data described in one or more CSV files, you can use the OpenFisca Python API.

Application: calculate a population’s income tax from a CSV file

Let’s say you are using the country-template, which describes the legislation of a yet to be country.

Let’s also say you have the following data.csv and that you want to calculate income_tax for all persons:

  1. Install the required libraries, by running in your console:
$ python --version # Python 3.7.0 or greater should be installed on your computer
$ pip install --upgrade pip openfisca_country_template pandas ipython
$ ipython
  1. Load the country-template legislation and, then, the content of the data.csv file with the pandas library:
In [1]: from openfisca_country_template import CountryTaxBenefitSystem

In [2]: import pandas as pandas

In [3]: tax_benefit_system = CountryTaxBenefitSystem()

In [4]: data = pandas.read_csv('./data.csv')  # pandas.DataFrame object

In [5]: length = len(data)  # ignores CSV header

You can now access the person_salary column values:

In [6]: data.person_salary
0     2694
1     2720
2     1865
3     1941
4     2393
5     3008
6     2286
7     3386
8     2929
9     3981
10    3643
11    2078
Name: person_salary, dtype: int64
  1. Build a simulation according to your data’s length:
In [7]: from openfisca_core.simulation_builder import SimulationBuilder

In [8]: simulation = SimulationBuilder().build_default_simulation(tax_benefit_system, length)
  1. Configure the simulation and calculate the income_tax variable for all persons on the same period:
In [9]: import numpy as numpy

In [10]: period = '2018-01'

# match data from the 'person_salary' column
# with the 'salary' variable of our yet to be country's tax-benefit system
In [11]: simulation.set_input('salary', period, numpy.array(data.person_salary))

In [12]: income_tax = simulation.calculate('income_tax', period)
  1. You are all set! The income_tax has been calculated for each person on your data.csv file.

Persons’ order is kept:

In [13]: data.person_id.values
Out[13]: array([ 1,  2,  3,  4,  5,  6,  7,  8,  9, 10, 11, 12])

And income_tax is an instance of numpy.ndarray:

In [14]: income_tax
array([404.1    , 408.00003, 279.75   , 291.15002, 358.95   , 451.2    ,
       342.90002, 507.90002, 439.35   , 597.15   , 546.45   , 311.7    ],

In [15]: income_tax.item(2)  # person_id == 3
Out[15]: 279.75