We welcome contributions to petitRADTRANS! If you want to contribute a new capability to the code, especially if it is something more involved, please notify the development team before. This is such that we can gauge whether your contribution can or should be merged into pRT.

Suggestions and reporting issues

We always aim to enhance petitRADTRANS, so do not hesitate to report bugs or propose new features or other suggestions. The preferred way in both cases is to create a new issue on the petitRADTRANS gitlab. In that case, please take the time to read the guidelines below.

Alternatively, you can directly contact members of the development team via e-mail.

Guidelines to report an issue

  • Ensure that the issue is petitRADTRANS-related (see below).

  • Use a clear title for the issue.

  • Add a few lines to describe your issue.

  • Add relevant information.

  • Always include an example that can be used by the developers to reproduce your issue.

  • For large scripts or console outputs (more than ~20 lines), please use attached files.

  • If your issue is resolved (by yourself or a developer), please report it, especially if you solved the issue yourself: this can help other people and also the developer team.

While we are happy to help everyone in need, please only report direct petitRADTRANS-related issues. Most of the time issues from, for example, setups (Mac, Conda, compilers, …) are not related to and cannot be fixed by petitRADTRANS. For these issues we recommend Q&A platforms such as stackoverflow. If you still encounter difficulties, contact the petitRADTRANS team and we will do our best to help you.

Adding new opacities

You can add new opacities following the instruction in the corresponding section.

If you add opacities which are not available through the ExoMol website, and if you are particularly nice, you can share these opacities with us. We would then make them available to the other petitRADTRANS users via this website, while properly attributing your contribution.

Contribute code

Development setup and how to submit changes


If you plan for a large addition that takes a lot of time to develop, please inform the development team early. This is to ensure that we are aware of your project and can gauge whether it should be incorporated into petitRADTRANS. Please note that we cannot guarantee that external developments will be merged into the package before this vetting process. If we believe that pRT will benefit from your addition, we may even suggest to integrate you into the development team for a better coordination of development efforts.

If you would like to make a fix or add a feature to petitRADTRANS, you may proceed as follows:

  1. Install Git.

  2. Sign up to Gitlab.

  3. Fork petitRADTRANS from the main repository.


    you may directly create a new branch (step 10) instead of a fork.

  4. Clone your fork to work locally.

  5. Go inside the cloned directory. Add an upstream remote and fetch it with:
    git remote add upstream
    git fetch upstream
  6. Set your main branch to track upstream using.
    git branch -u upstream/master master


    Points 5 and 6 ensure that your fork stays connected with the “official” pRT repository and that you can always incorporate pRT changes into your fork by typing e.g. git merge upstream/master.

  7. Follow the petitRADTRANS installation instructions to install your fork. Once you are setup, use the following command:
    pip install -e .[test] --no-build-isolation
  8. Install tox.

  9. Check that the test suite is working by executing tox in the main directory of you fork.

  10. Create a new branch using git switch --create branch-name.

  11. Make your changes.

  12. Regularly commit your changes using git commit -m 'Concise description of the change'.

  13. Before pushing, always test your changes by executing tox.

  14. Push to your branch using git push.

  15. Create a merge request from your fork, targeting the upstream.

You may contact by mail members of the development team to inform them about your (future) merge request at any time in the development process. Stay available in case modifications are requested by the development team before merging your branch.


Make atomic Git commits, accompanying comments should be short but descriptive, starting with a verb in the infinitive.

Guidelines before creating a merge request

  • All code should have tests.

  • All code should be documented, functions intended to be used by the user must at least have complete docstrings.

  • The test suite (including eventually the tests of your new feature) must raise no error. This include flake8/style errors. You may ask the developer team in case you need help solving these errors.

  • The test suite must raise no petitRADTRANS-related warnings. Sometimes warnings may be raised by external libraries, these can be ignored.

  • Ensure that you respected the stylistic guidelines.

Style Guide

These guidelines are intended to create a consistency within the code, facilitating usage, readability, and maintenance in the long term.

In general, look at existing code for guidance. Before committing, take the time to re-read your code and ensure that you respected the guidelines. Fixing existing code to make it more inline with those guidelines is strongly encouraged.

  • It is strongly encouraged to use an IDE such as PyCharm (you can use the free community edition) to help you respect the code style.

  • Set up your editor to follow PEP 8. In PyCharm, this is enabled by default.

  • When implementing an equation or using a specific value, always indicate the source (DOI) in docstrings or comments.

  • Respect the DRY convention: never copy paste lines of code, create a new function instead if necessary.

  • Do not use magic numbers:
    # Yes
    my_magic_number = 27.849846  # source if relevant, and explanation if a descriptive name is not enough
    if value > my_magic_number:
    # No
    if value > 27.849846:
  • Name conventions:
    • Use extensive naming: always prefer e.g. temperature to t. Names should be as descriptive as possible and should be understood without context, while reasonably long.

    • Function names in most cases should start with a verb in the infinitive describing the function’s purpose.

    • Names for arrays (or lists, dicts, etc.) containing multiple elements must be plural.

    • Use get_ and set_ only for simple functions that perform no calculation.

    • Use compute_ for class functions that are static or module functions that calculate something.

    • Use calculate_ only for class functions (first argument self) that calculate something.

    • Use <start>2<end> for conversions (e.g., from one unit to another as in light_year2parsec).

    • Use save and load for I/O functions involving locally stored files.

    • You may begin a function’s name with from_ only for classmethod.

    • Functions that are not intended to be used by users, or outside their module/class must start with a single _.

    • Functions that have no purposes outside their context or used only once in the code must start with __.

  • Functions in a module or attribute in a class should be declared in alphanumerical order. The character _ is the first character in that order.

  • Indented blocks (e.g. if/else, for, etc.) should be separated from other code with a blank line (above and below).
    # Yes
    # Eventually, a comment describing what the block is doing
    if condition:
    # No
    if condition:
  • Function calls or object instantiations should explicitly display the arguments, one by line, unless there is 1 or less argument or the function is from an external library:
    # Yes
    # No
    function(value_1, argument_2=value_2,
             argument_3=value_3, argument_4=value_4,
    # No (unless the function has 1 or less argument or is from an external library)
    function(argument_1=value_1, argument_2=value_2, ...)
    function(value_1, argument_2=value_2, ...)
    function(value_1, value_2, ...)
  • Use parenthesis instead of \ for line breaks:
    # Yes
    a_very_long_equation = (
        * term_2
        * term_3
    # No
    a_very_long_equation = \
        term_1 \
        * term_2 \
        * term_3
  • Functions intended to be used by users should have type hints.

  • Avoid extremely long functions. As a rule of thumb, if a function is more than 100 lines long, break it into smaller functions.

  • Docstrings:
    • must follow the Google style.

    • must follow the normal sentence rules for docstrings.

  • Comments (starting with # on Python):
    • must never end with a dot,

    • on a line without code, must start with an uppercase,

    • on a line with code, must start with a lowercase,

    • may be exceed the line character limit (120) if they are on a line with code or unbreakable (e.g. URL), in that case add # noqa E501 at the end of the comment to signal flake8 that this is expected.

  • If you are using PyCharm, fix all errors, warnings, and weak warnings, with the following exceptions:
    • errors related to the import of Fortran extensions can be ignored as long as the code works and does not produce warnings.

    • warnings related to expected types or not found references can be ignored if the warning is related to an external library or a fortran function, as long as the code works and does not produce warnings.

    • weak warnings related to not using kwargs can be ignored: this is part of the code architecture.

The petitRADTRANS test suite

How to run the tests?

  1. Install tox.

  2. Within the petitRADTRANS root directory, execute the command tox in a console.

All the tests within the “tests” directory will be executed. A summary will be available at the end of the procedure, including test code coverage.


Before a push, tox should always be run.

Conda: running the tests

When using conda environments, you must install tox-conda prior to running the tox test suite. Additionally, you may run into issues with package versions and getting the test suite to run properly, in particular with the numba package. You will need to conda install numba, even if you have already installed the package through pip. We also suggest running tox for specific python versions, rather than automatically running on the base version installed on your system. At the very least, you should run tests on the oldest version currently supported by pRT (python 3.9 as of 2024), as well as the most recent version.

Below an example to tox test the code with flake8 and python 3.11:

conda create --name toxfun python=3.11
conda activate toxfun
pip install tox
pip install tox-conda
conda install numba
tox -e flake8
tox -e py311


The tox configuration is set within the “setup.cfg” file.

Tox will automatically execute any function in any module across all the project whose name is starting with test_. To keep the code clean, the tests should by default be put within the “tests” directory. The structure of this directory is as follows:
├── data                           <- contains the test parameters
|   ├── config_test_radtrans.json  <- the parameters for the test suite
|   ├── <several .npz/.dat files>  <- data files used in tests
|   └── test_stats.json            <- results of the last validated retrieval test
├── errors                         <- if an AssertionError is raised, results will be sent here for diagnostic
├── references                     <- contains the test reference files, storing results from the last validated test
|   └── <numerous .h5 files>       <- results of the last validated retrieval test
├── results                        <- results of the last retrieval test
├──                    <- init file (empty)
├──                   <- module containing the Benchmark class, used to compare the results
├──                     <- loaded in tests modules in order to ensure that the local version of petitRADTRANS is tested
├── <numerous test modules>        <- modules containing the testing functions
└──                       <- module containing initialisation and comparison functions

The test functions that will be executed by tox are in the test modules. To minimize loading time, there is one module per required Radtrans object. Other test modules are here to sort tests. Most modules import module context to ensure that the local version of the code is tested. There is also a relative_tolerance variable set at the beginning to indicate the relative tolerance when comparing the results with the last validated ones.

In order to keep things clean in the long run: if a test goes wrong, avoid increasing the tolerance. Instead, try first to understand the origin of the difference. It is your responsibility as a developer to understand and explain changes in results coming from the changes you made within the code.

Most of the tests consist of calling a petitRADTRANS function, and to compare the result with the last validated one. If an AssertionError is raised, an error file is automatically generated in the “errors” directory. The error file is a .h5 file containing 6 datasets:

  • test_outputs, the results of the current test,

  • reference_outputs, the results of the last validated test,

  • prt_version, the version of petitRADTRANS used to generate the last validated test,

  • relative_tolerance, the relative tolerance used to compare the results,

  • absolute_tolerance, the absolute tolerance used to compare the results.

  • date, the date of the test.

In addition, the test will compare the inputs of the tested function. If a discrepancy is detected, an error file is automatically generated in the “errors” directory. The error file is a .h5 file containing 6 datasets:

  • invalid_test_parameters, the invalid inputs used for the current test,

  • reference_parameters, the corresponding inputs used for the last validated test,

  • prt_version, the version of petitRADTRANS used to generate the last validated test,

  • relative_tolerance, the relative tolerance used to compare the results,

  • absolute_tolerance, the absolute tolerance used to compare the results.

  • date, the date of the test.

These files can be used for diagnostic.

Creating a new test

Tests are used both to ensure that every functionality of the code work, but also that they work as expected. It follows that a proper test should:

  • Ensure that a function runs.

  • Ensure that the results from the function is what is expected.

  • Provides an easy way to check the results if they are not expected, and to track the changes that could have led to this discrepancy.

  • Be easily reproducible.

  • Be as fast as possible without compromising with functionality testing.

In order to create a test, you can use the petitRADTRANS tools and follow these steps:

  1. If you need a Radtrans object (or equivalent), first check if there is one that already suits your need in the existing test modules.

  2. If relevant, create a new test module, beginning with test. At the top of the module, put:
    from .benchmark import Benchmark
    from .context import petitRADTRANS
  3. Create your test function (starting with test_). Be as expansive as possible when choosing the name, to make it easier to understand what went wrong if it fails. For the same reason, most of the time you would want to have one functionality tested per test function. The function should have no arguments.

  4. Add lines to compare your results with previous ones. To do so, it is highly recommended to use the following structure:
    def test_my_feature():
        benchmark = Benchmark(
  5. Check the dictionary within utils.make_petitradtrans_test_config_file and look for parameters that you can use in your test function, if possible without editing them. If necessary, add key/value pairs to this dictionary. The added values should be small (i.e. no size 10+ array). In general, keep your inputs as small as possible to make tests faster and limit data storage on git. Any larger input (max ~100 kB) should be stored outside this file in the “data” directory. Exception is made for files inside the petitRADTRANS “input_data” directory, that must not be stored on the git.

  6. In a python console, execute:
    from tests.test_my_new_module import test_my_feature  # this will automatically re-generate the parameter file if needed
    test_my_feature()  # generate the reference comparison file, then test the function
  7. Launch tox to be sure that everything went right.


If your test failed with tox:

  • You can execute your test function in a Python console to help you debug it faster.

  • If you used the recommended Benchmark workflow, you can also use the generated error files to help you.

Resetting all reference files

In rare cases, for example when pushing a new major version, it might be interesting to reset all reference files. This operation should not be taken lightly as this can have significant consequences on the code’s reproducibility and behaviour. To easily do this operation, execute the following:

from tests.benchmark import Benchmark

Before the reset, you will go through a checklist. Please take the time to read it. If you do not meet all the criteria, cancel the operation.


petitRADTRANS adheres to Semantic Versioning.

The code’s version must be updated in the following files:



  • pyproject.toml

petitRADTRANS comes with a changelog that is regularly updated with the most notable changes from the code. The format is based on Keep a Changelog.

In the changelog, changes are ordered by perceived importance for the user. Changes or fixes internal to an alpha or beta version are not indicated.