This guide assumes you have forked and checked-out the repository. It is recommended that you install Hydra in a virtual environment like conda or virtualenv.

Environment setup

Install Miniconda and create an empty Conda environment with:

conda create -n hydra37 python=3.7 -y

Activate the environment:

conda activate hydra37

From the source tree, install Hydra in development mode with the following command:

pip install -e .[dev] -e .

Pre commit hooks

It is highly recommended that you install pre commit hooks into your local git repository.

pre-commit install

Pre commit hooks can help you catch problems before you push your pull request.


  • black : automatic code formatting for Python
  • flake8: pep8 compliance checker for Python, this includes copyright header verification. any PR that does not pass black and flake8 will fail the automated testing.


There are two ways to run the tests:

With pytest

use pytest at the repository root to run all the Hydra core tests. To run the tests of individual plugins, use pytest plugins/NAME.

With nox

Nox is a test automation tool that is used by the CI to test Hydra under multiple Python versions with a single command.

To trigger a full nox run, just run nox.

You may want to run specific nox sessions as well to speed things up. nox -l will list all available sessions. You can use nox -s NAME to run a specific session.

For example:

  • nox -s test_core will test Hydra core on all supported Python versions
  • nox -s lint will lint the code in both Python 2 and Python 3.
  • nox -s coverage will run the code coverage tool

NEWS Entries

The NEWS.rst file is managed using towncrier and all non trivial changes must be accompanied by a news entry.

To add an entry to the news file, first you need to have created an issue describing the change you want to make. A Pull Request itself may function as such, but it is preferred to have a dedicated issue (for example, in case the PR ends up rejected due to code quality reasons).

Once you have an issue or pull request, you take the number and you create a file inside of the news/ directory named after that issue number with one of the following extensions:

  • removal : Removal of deprecation of a feature
  • feature : Addition of a new feature
  • bugfix : Fixing of a bug
  • docs : Addition or updates to documentation
  • plugin : Addition of changes to a plugin
  • config : Changes or addition to the configuration structure

If your issue or PR number is 1234 and this change is fixing a bug, then you would create a file news/1234.bugfix. PRs can span multiple categories by creating multiple files (for instance, if you added a feature and deprecated/removed the old feature at the same time, you would create news/NNNN.feature and news/NNNN.removal). Likewise if a PR touches multiple issues/PRs you may create a file for each of them with the exact same contents and Towncrier will deduplicate them.

Contents of a NEWS entry

The contents of this file are reStructuredText formatted text that will be used as the content of the news file entry. You do not need to reference the issue or PR numbers here as towncrier will automatically add a reference to all of the affected issues when rendering the news file.

In order to maintain a consistent style in the NEWS.rst file, it is preferred to keep the news entry to the point, in sentence case, shorter than 80 characters and in an imperative tone -- an entry should complete the sentence "This change will ...". In rare cases, where one line is not enough, use a summary line in an imperative tone followed by a blank line separating it from a description of the feature/change in one or more paragraphs, each wrapped at 80 characters. Remember that a news entry is meant for end users and should only contain details relevant to an end user.

Last updated on 10/19/2019 by Omry Yadan