Developer’s Guide For AiiDA

Python style

When writing python code, a more than reasonable guideline is given by the Google python styleguide The documentation should be written consistently in the style of sphinx.

And more generally, write verbose! Will you remember after a month why you had to write that check on that line? (Hint: no) Write comments!


You can check your code style and other important code errors by using Pylint. Once installed you can run Pylint from the root source directory on the code using the command:

pylint aiida

The most important part is the summary under the Messages table near the end.

Version number

The AiiDA version number is stored in aiida/ Make sure to update this when changing version number.

Inline calculations

If an operation is extremely fast to be run, this can be done directly in Python, without being submitted to a cluster. However, this operation takes one (or more) input data nodes, and creates new data nodes, the operation itself is not recorded in the database, and provenance is lost. In order to put a Calculation object inbetween, we define the InlineCalculation class, that is used as the class for these calculations that are run “in-line”.

We also provide a wrapper (that also works as a decorator of a function), make_inline(). This can be used to wrap suitably defined function, so that after their execution, a node representing their execution is stored in the DB, and suitable input and output nodes are also stored.


See the documentation of this function for further documentation of how it should be used, and of the requirements for the wrapped function.

Database schema

The Django database schema can be found in aiida.backends.djsite.db.models.

If you need to change the database schema follow these steps:

  1. Make all the necessary changes to aiida.backends.djsite.db.models

  2. Create a new migration file. From aiida/backends/djsite, run:

    python makemigrations

    This will create the migration file in aiida/backends/djsite/db/migrations whose name begins with a number followed by some description. If the description is not appropriate then change to it to something better but retain the number.

  3. Open the generated file and make the following changes:

    from aiida.backends.djsite.db.migrations import update_schema_version
    SCHEMA_VERSION = # choose an appropriate version number
                     # (hint: higher than the last migration!)
    class Migration(migrations.Migration):
      operations = [
  1. Change the LATEST_MIGRATION variable in aiida/backends/djsite/db/migrations/ to the name of your migration file:

    LATEST_MIGRATION = '0003_my_db_update'

    This let’s AiiDA get the version number from your migration and make sure the database and the code are in sync.

  2. Migrate your database to the new version, (again from aiida/backends/djsite), run:

    python migrate

Commits and GIT usage

In order to have an efficient management of the project development, we chose to adopt the guidelines for the branching model described here. In particular:

  • The main branch in which one should work is called develop
  • The master branch is reserved for releases: every commit there implies a new release. Therefore, one should never commit directly there (except once per every release).
  • New releases should also be tagged.
  • Any new modification requiring just one commit can be done in develop
  • mid-to-long development efforts should be done in a branch, branching off from develop (e.g. a long bugfix, or a new feature)
  • while working on the branch, often merge the develop branch back into it (if you also have a remote branch and there are no conflicts, that can be done with one click from the GitHub web interface, and then you just do a local ‘git pull’)
  • remember to fix generic bugs in the develop (or in a branch to be then merged in the develop), not in your local branch (except if the bug is present only in the branch); only then merge develop back into your branch. In particular, if it is a complex bugfix, better to have a branch because it allows to backport the fix also in old releases, if we want to support multiple versions
  • only when a feature is ready, merge it back into develop. If it is a big change, better to instead do a pull request on GitHub instead of directly merging and wait for another (or a few other) developers to accept it beforehand, to be sure it does not break anything.

For a cheatsheet of git commands, see here.


Before committing, always run:

verdi devel tests

to be sure that your modifications did not introduce any new bugs in existing code. Remember to do it even if you believe your modification to be small - the tests run pretty fast!


Running the tests

To run the tests, use the:

verdi devel tests

command. You can add a list of tests after the command to run only a selected portion of tests (e.g. while developing, if you discover that only a few tests fail). Use TAB completion to get the full list of tests. For instance, to run only the tests for transport and the generic tests on the database, run:

verdi devel tests aiida.transport db.generic

The test-first approach

Remember in best codes actually the tests are written even before writing the actual code, because this helps in having a clear API.

For any new feature that you add/modify, write a test for it! This is extremely important to have the project last and be as bug-proof as possible. Even more importantly, add a test that fails when you find a new bug, and then solve the bug to make the test work again, so that in the future the bug is not introduced anymore.

Remember to make unit tests as atomic as possible, and to document them so that other developers can understand why you wrote that test, in case it should fail after some modification.

Creating a new test

There are three types of tests:

  1. Tests that do not require the usage of the database (testing the creation of paths in k-space, the functionality of a transport plugin, ...)
  2. Tests that require the database, but do not require submission (e.g. verifying that node attributes can be correctly queried, that the transitive closure table is correctly generated, ...)
  3. Tests that require the submission of jobs

For each of the above types of tests, a different testing approach is followed (you can also see existing tests as guidelines of how tests are written):

  1. Tests are written inside the package that one wants to test, creating a file. For each group of tests, create a new subclass of unittest.TestCase, and then create the tests as methods using the unittests module. Tests inside a selected number of AiiDA packages are automatically discovered when running verdi devel tests. To make sure that your test is discovered, verify that its parent module is listed in the base_allowed_test_folders property of the Devel class, inside aiida.cmdline.commands.devel.

    For an example of this type of tests, see, e.g., the aiida.common.test_utils module.

  2. In this case, we use the testing functionality of Django, adapted to run smoothly with AiiDA.

    To create a new group of tests, create a new python file under aiida.backends.djsite.db.substests, and instead of inheriting each class directly from unittest, inherit from aiida.backends.djsite.db.testbase.AiidaTestCase. In this way:

    1. The Django testing functionality is used, and a temporary database is used
    2. every time the class is created to run its tests, default data are added to the database, that would otherwise be empty (in particular, a computer and a user; for more details, see the code of the AiidaTestCase.setUpClass() method).
    3. at the end of all tests of the class, the database is cleaned (nodes, links, ... are deleted) so that the temporary database is ready to run the tests of the following test classes.


    it is extremely important that these tests are run from the verdi devel tests command line interface. Not only this will ensure that a temporary database is used (via Django), but also that a temporary repository folder is used. Otherwise, you risk to corrupt your database data. (In the codes there are some checks to avoid that these classes are run without the correct environment being prepared by verdi devel tests.)

    Once you create a new file in aiida.backends.djsite.db.substests, you have to add a new entry to the db_test_list inside aiida.backends.djsite.db.testbase module in order for verdi devel tests to find it. In particular, the key should be the name that you want to use on the command line of verdi devel tests to run the test, and the value should be the full module name to load. Note that, in verdi devel tests, the string db. is prepended to the name of each test involving the database. Therefore, if you add a line:

    db_test_list = {
      'newtests': 'aiida.backends.djsite.db.subtests.mynewtestsmodule',

    you will be able to run all all tests inside aiida.backends.djsite.db.subtests.mynewtestsmodule with the command:

    verdi devel tests db.newtests


    If in the list of parameters to verdi devel tests you add also a db parameter, then all database-related tests will be run, i.e., all tests that start with db. (or, if you want, all tests in the db_test_list described above).


    By default, the test database is created using an in-memory SQLite database, which is much faster than creating from scratch a new test database with PostgreSQL or SQLite. However, if you want to test database-specific settings and you want to use the same type of database you are using with AiiDA, set the tests.use_sqlite global property to False:

    verdi devel setproperty tests.use_sqlite false
  3. These tests require an external engine to submit the calculations and then check the results at job completion. We use for this a continuous integration server, and the best approach is to write suitable workflows to run simulations and then verify the results at the end.

Special tests

Some tests have special routines to ease and simplify the creation of new tests. One case is represented by the tests for transport. In this case, you can define tests for a specific plugin as described above (e.g., see the aiida.transport.plugins.test_ssh and aiida.transport.plugins.test_local tests). Moreover, there is a test_all_plugins module in the same folder. Inside this module, the discovery code is adapted so that each test method defined in that file and decorated with @run_for_all_plugins is run for all available plugins, to avoid to rewrite the same test code more than once and ensure that all plugins behave in the same way (e.g., to copy files, remove folders, etc.).

Virtual environment

Sometimes it’s useful to have a virtual environment that separates out the AiiDA dependencies from the rest of the system. This is especially the case when testing AiiDA against library versions that are different from those installed on the system.

First, install virtualenv using pip:

pip install virtualenv

Basic usage

  1. To create a virtual environment in folder venv, while in the AiiDA directory type:

    virtualenv venv

    This puts a copy of the Python executables and the pip library within the venv folder hierarchy.

  2. Activate the environment with:

    source venv/bin/activate

    Your shell should now be prompt should now start with (venv).

  3. (optional) Install AiiDA:

    pip install .
  4. Deactivate the virtual environment:


Deprecated features, renaming, and adding new methods

In case a method is renamed or removed, this is the procedure to follow:

  1. (If you want to rename) move the code to the new function name. Then, in the docstring, add something like:

    .. versionadded:: 0.7
       Renamed from OLDMETHODNAME
  2. Don’t remove directly the old function, but just change the code to use the new function, and add in the docstring:

    .. deprecated:: 0.7
       Use :meth:`NEWMETHODNAME` instead.

    Moreover, at the beginning of the function, add something like:

    import warnings
        "OLDMETHODNAME is deprecated, use NEWMETHODNAME instead",

    (of course, replace OLDMETHODNAME and NEWMETHODNAME with the correct string, and adapt the strings to the correct content if you are only removing a function, or just adding a new one).