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Version: 0.11


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 hydra38 python=3.8 -y

Activate the environment:

conda activate hydra38

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

pip install -e ".[dev]" -e .


Hydra is using a test automation tool called nox to manage tests, linting, code coverage etc. nox will run all the configured sessions. You can see the full list of nox sessions with nox -l and run specific sessions with nox -s NAME (you may need to quote the session name in some cases)

Code style guide​

The code need to pass verification by the following tools:

  • black . : Automatic code formatting for Python
  • flake8 : PEP8 compliance checker for Python, this includes copyright header verification
  • isort . : Ensure imports are sorted properly
  • mypy --strict . : Ensures code passes strict type checking

The easiest way to run all the required verifications is with nox -s lint.

It is also recommended that you install pre-commit hooks (use pre-commit install), this will ensure that those tests are ran just before you commit your code.

Any pull request that does not pass the linting will fail the automated testing.


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​

See nox -l. a few examples:

  • nox -s test_core will test Hydra core on all supported Python versions
  • nox -s "test_core-3.6(pip install)" : Test on Python 3.6 with pip install as installation method
  • nox -s "test_plugins-3.8(pip install -e)" : Test plugins on Python 3.8 with pip install -e as installation method

NEWS Entries​

The 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 or deprecation of a feature
  • feature : New feature
  • bugfix : Bug fix
  • plugin : New plugin, or an update to an existing plugin
  • config : Changes or addition to the configuration structure of Hydra
  • docs : Major addition or updates to documentation

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 is markdown 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 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.