Contributing to IOSACal#


IOSACal is written in Python 3, and it makes heavy use of the NumPy library for the internal management of calibration curves and calibrated samples. Calibration curves, radiocarbon dates and calibrated curves are handled internally as ndarray objects. ndarray objects are matrices that can be easily manipulated through slicing, flipping, summing and other typical operations.

Generation of plots is done through Matplotlib, another Python library built on top of NumPy. Matplotlib can natively read ndarray objects and plot them in a graphical form. Far from being just a set of plotting functions, Matplotlib allows the drawing of complex plots like those created by IOSACal.

Development happens in a public git repository at Codeberg, the free home for free projects. The default branch name is main.

Code of Conduct#

All contributors to IOSACal are subject to the project’s Code of Conduct, that is found in the root of the Git repository as

Please take some time to read it and understand how it regulates participation in the project.

Codebase structure#

The iosacal directory in the root of the Git repository is a Python package that contains the following source code files:

  • is first of all there to declare that this directory is a Python package. It also imports three objects (R, combine and iplot) so that they can be imported directly from the root package with from iosacal import R - that is enough to calibrate a date when using a Python interpreter. And it contains the current version that is propagated to other parts of the program.

  • contains the command line app, based on Click

  • contains the main classes to instantiate calibration curves and radiocarbon determinations, and functions that work directly on them like combine

  • contains functions to compute Highest Posterior Density and helper classes to format the resulting confidence intervals

  • contains two large functions based on Matplotlib that are respectively dedicated to plotting a single date or multiple (“stacked”) dates. The small iplot function is useful for usage with Jupyter notebooks

  • contains functions and classes for working with Sum of Probability Distributions of calibrated dates

  • contains one function to format calibration results for output to a terminal or a Markdown document

  • the data subdirectory contains the calibration curves in the standard .14c format.

Tests are in a separate directory called tests in the root of the Git repository. Each file corresponds to one of the modules listed above and has the name prefixed with test_, such as

Documentation is in the docs directory and is a collection of files in reStructured Text format, for use with Sphinx. There is also a file called .readthedocs.yaml in the root of the Git repository, that contains some settings for Read the Docs, the service that publishes the formatted documentation you are probably reading right now. If you’re contributing changes to the source code, please always check that the documentation is updated and include relevant changes to the documentation as well.


Contributing to IOSACal can be done by suggesting improvements or pointing out bugs and limitations of the program. This kind of contribution works by opening a new issue at . Please always open a new issue to let other contributors know that you’re working on a specific problem.

New commits should not be directly pushed to the main branch, but proposed for merging with a pull request. The pull request allows some discussion of the proposed changes among maintainers. The main branch is locked and can only be updated by merging other branches.

Another related point is that commit messages should be as informative as possible. If a commit fixes a bug, there should be some description of the fixed bug. Each commit must be “atomic” and bring a self-contained change, not many unrelated edits (even to the same file).

You will need Git to clone the repository on your development machine. However, if you’re not familiar with Git or you don’t want to open an account specifically for contributing, you can send the modified files by email or attach them to the issue.

Coding guidelines#

All Python source must be formatted with black with the default settings, which makes formatting very straightforward: you just need to run it before committing your changes to git and all code is automatically adapted to the “standard” code style.

Black can be run manually, but for regular contributors it is easier to run it automatically with pre-commit. Once pre-commit is installed, activate it for your local repository using the provided configuration file:

pre-commit install


The tests in the tests directory are meant to be run before committing your changes.

To run the tests you need pytest: install it in a clean development environment and run:


without any argument. If all goes well, a success message will greet you. If you see any failure, it means something you have changed causes IOSACal to behave abnormally. Please fix the errors before committing, if you need help open an issue.


The IntCal calibration curves have a varying resolution. For example, in IntCal09 data spacing changes from 5 years for the range from 0 to 11.2 to cal kBP, 10 yrs for 11.2–15 cal kBP, 20 yrs for 15–25 cal kBP, 50 yrs for 25–40 cal kBP, and 100 yrs for 40–50 cal kBP [REI2009]. Other curves follow a similar pattern.

This means that the output intervals would follow these limitations. IOSACal uses the interp function of NumPy to perform linear interpolation of the calibration curves and obtain more fine-grained results, particularly concerning probability intervals.


Reimer PJ, Baillie MGL, Bard E, Bayliss A, Beck JW, Blackwell PG, Bronk Ramsey C, Buck CE, Burr GS, Edwards RL, Friedrich M, Grootes PM, Guilderson TP, Hajdas I, Heaton TJ, Hogg AG, Hughen KA, Kaiser KF, Kromer B, McCormac FG, Manning SW, Reimer RW, Richards DA, Southon JR, Talamo S, Turney CSM, van der Plicht J, Weyhenmeyer CE. 2009. IntCal09 and Marine09 radiocarbon age calibration curves, 0–50,000 years cal BP. Radiocarbon 51(4):1111–50.