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OpenFisca Core

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OpenFisca is a versatile microsimulation free software. Check the online documentation for more details.

This package contains the core features of OpenFisca, which are meant to be used by country packages such as OpenFisca-France. Bootstrapping your own country package should not take more than 5 minutes: check our country package template.


OpenFisca runs on Python 3.7. More recent versions should work, but are not tested.


If you're developping your own country package, you don't need to explicitly install OpenFisca-Core. It just needs to appear in your package dependencies.

If you want to contribute to OpenFisca-Core itself, welcome! To install it locally in development mode run the following commands:

git clone
cd openfisca-core
pip install --editable .[dev] --use-deprecated=legacy-resolver


To run the entire test suite:

make test

To run all the tests defined on a test file:

pytest tests/core/

To run a single test:

pytest tests/core/ -k test_parameter_for_period


This repository adheres to a certain coding style, and we invite you to follow it for your contributions to be integrated promptly.

Style checking is already run with make test. To run the style checker alone:

make check-style

To automatically style-format your code changes:

make format-style

To automatically style-format your code changes each time you commit:

touch .git/hooks/pre-commit
chmod +x .git/hooks/pre-commit

tee -a .git/hooks/pre-commit << END
# Automatically format your code before committing.
exec make format-style

Serving the API

OpenFisca-Core provides a Web-API. It is by default served on the 5000 port.

To run it with the mock country package openfisca_country_template and another port value such as 2000, run:

openfisca serve --country-package openfisca_country_template --port 2000

To read more about the openfisca serve command, check out its documentation.

By default, the Web API uses 3 workers to avoid this issue. Without it, AJAX requests from Chrome sometimes take more than 20s to process. You can change the number of workers by specifying a --workers k option.

You can test that the API is running by executing the command:

curl http://localhost:2000/parameters

For more information about endpoints and input formatting, see the official documentation.


The OpenFisca Web API comes with an optional tracker which allows you to measure the usage of the API.

Tracker installation

The tracker is not installed by default. To install it, run:

pip install openfisca_core[tracker] --use-deprecated=legacy-resolver # Or `pip install --editable ".[tracker]"` for an editable installation

Tracker configuration

The tracker is activated when these two options are set:

  • --tracker-url: An URL ending with piwik.php. It defines the Piwik instance that will receive the tracking information. To use the main OpenFisca Piwik instance, use
  • --tracker-idsite: An integer. It defines the identifier of the tracked site on your Piwik instance. To use the main OpenFisca piwik instance, use 4.
  • --tracker-token: A string. It defines the Piwik API Authentification token to differentiate API calls based on the user IP. Otherwise, all API calls will seem to come from your server. The Piwik API Authentification token can be found in your Piwik interface, when you are logged.

For instance, to run the Web API with the mock country package openfisca_country_template and the tracker activated, run:

openfisca serve --country-package openfisca_country_template --port 5000 --tracker-url --tracker-idsite 4 --tracker-token $TRACKER_TOKEN


OpenFisca core engine. See other repositories for countries-specific code & data.





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