Dask is a community maintained project. We welcome contributions in the form of bug reports, documentation, code, design proposals, and more. This page provides resources on how best to contribute.
Dask strives to be a welcoming community of individuals with diverse backgrounds. For more information on our values, please see our code of conduct and diversity statement
Where to ask for help¶
Dask conversation happens in the following places:
Dask Discourse forum: for usage questions and general discussion
Stack Overflow #dask tag: for usage questions
GitHub Issue Tracker: for discussions around new features or established bugs
Dask Community Slack: for real-time discussion
For usage questions and bug reports we prefer the use of Discourse, Stack Overflow and GitHub issues over Slack chat. Discourse, GitHub and Stack Overflow are more easily searchable by future users, so conversations had there can be useful to many more people than just those directly involved.
Separate Code Repositories¶
Dask maintains code and documentation in a few git repositories hosted on the
dask organization, https://github.com/dask. This includes the primary
repository and several other repositories for different components. A
non-exhaustive list follows:
https://github.com/dask/dask: The main code repository holding parallel algorithms, the single-machine scheduler, and most documentation
https://github.com/dask/distributed: The distributed memory scheduler
https://github.com/dask/dask-ml: Machine learning algorithms
https://github.com/dask/s3fs: S3 Filesystem interface
https://github.com/dask/gcsfs: GCS Filesystem interface
https://github.com/dask/hdfs3: Hadoop Filesystem interface
Git and GitHub can be challenging at first. Fortunately good materials exist on the internet. Rather than repeat these materials here, we refer you to pandas’ documentation and links on this subject at https://pandas.pydata.org/docs/dev/development/contributing.html
The community discusses and tracks known bugs and potential features in the GitHub Issue Tracker. If you have a new idea or have identified a bug, then you should raise it there to start public discussion.
If you are looking for an introductory issue to get started with development, then check out the “good first issue” label, which contains issues that are good for starting developers. Generally, familiarity with Python, NumPy, pandas, and some parallel computing are assumed.
Make a fork of the main Dask repository and clone the fork:
git clone https://github.com/<your-github-username>/dask.git cd dask
You should also pull the latest git tags (this ensures
pip’s dependency resolver
can successfully install Dask):
git remote add upstream https://github.com/dask/dask.git git pull upstream main --tags
Contributions to Dask can then be made by submitting pull requests on GitHub.
From the top level of your cloned Dask repository you can install a local version of Dask, along with all necessary dependencies, using pip or conda
python -m pip install -e ".[complete,test]"
conda env create -n dask-dev -f continuous_integration/environment-3.10.yaml conda activate dask-dev python -m pip install --no-deps -e .
Contributing to Code¶
Dask maintains development standards that are similar to most PyData projects. These standards include language support, testing, documentation, and style.
Dask supports Python versions 3.8, 3.9 and 3.10.
Name changes are handled by the
Dask employs extensive unit tests to ensure correctness of code both for today and for the future. Test coverage is expected for all code contributions.
Tests are written in a py.test style with bare functions:
def test_fibonacci(): assert fib(0) == 0 assert fib(1) == 0 assert fib(10) == 55 assert fib(8) == fib(7) + fib(6) for x in [-3, 'cat', 1.5]: with pytest.raises(ValueError): fib(x)
These tests should compromise well between covering all branches and fail cases and running quickly (slow test suites get run less often).
You can run tests locally by running
py.test in the local dask directory:
You can also test certain modules or individual tests for faster response:
py.test dask/dataframe py.test dask/dataframe/tests/test_dataframe.py::test_rename_index
If you want the tests to run faster, you can run them in parallel using
py.test dask -n auto
Tests run automatically on GitHub Actions on every push to every pull request on GitHub.
Tests are organized within the various modules’ subdirectories:
dask/array/tests/test_*.py dask/bag/tests/test_*.py dask/bytes/tests/test_*.py dask/dataframe/tests/test_*.py dask/diagnostics/tests/test_*.py
For the Dask collections like Dask Array and Dask DataFrame, behavior is
typically tested directly against the NumPy or pandas libraries using the
import numpy as np import dask.array as da from dask.array.utils import assert_eq def test_aggregations(): nx = np.random.random(100) dx = da.from_array(nx, chunks=(10,)) assert_eq(nx.sum(), dx.sum()) assert_eq(nx.min(), dx.min()) assert_eq(nx.max(), dx.max()) ...
This technique helps to ensure compatibility with upstream libraries and tends
to be simpler than testing correctness directly. Additionally, by passing Dask
collections directly to the
assert_eq function rather than call compute
manually, the testing suite is able to run a number of checks on the lazy
User facing functions should roughly follow the numpydoc standard, including
Examples, and general explanatory prose.
By default, examples will be doc-tested. Reproducible examples in documentation
is valuable both for testing and, more importantly, for communication of common
usage to the user. Documentation trumps testing in this case and clear
examples should take precedence over using the docstring as testing space.
To skip a test in the examples add the comment
# doctest: +SKIP directly
after the line.
def fib(i): """ A single line with a brief explanation A more thorough description of the function, consisting of multiple lines or paragraphs. Parameters ---------- i: int A short description of the argument if not immediately clear Examples -------- >>> fib(4) 3 >>> fib(5) 5 >>> fib(6) 8 >>> fib(-1) # Robust to bad inputs ValueError(...) """
Docstrings are tested under Python 3.8 on GitHub Actions. You can test docstrings with pytest as follows:
py.test dask --doctest-modules
Docstring testing requires
graphviz to be installed. This can be done via:
conda install -y graphviz
Dask uses several code linters (flake8, black, isort, pyupgrade, mypy), which are
enforced by CI. Developers should run them locally before they submit a PR, through the
pre-commit run --all-files. This makes sure that linter versions and
options are aligned for all developers.
Optionally, you may wish to setup the pre-commit hooks to run automatically when you make a git commit. This can be done by running:
from the root of the Dask repository. Now the code linters will be run each time you
commit changes. You can skip these checks with
git commit --no-verify or with the
git commit -n.
Contributing to Documentation¶
Dask uses Sphinx for documentation, hosted on https://readthedocs.org .
Documentation is maintained in the RestructuredText markup language (
dask/docs/source. The documentation consists both of prose
and API documentation.
The documentation is automatically built, and a live preview is available, for each pull request submitted to Dask. Additionally, you may also build the documentation yourself locally by following the instructions outlined below.
How to build the Dask documentation¶
To build the documentation locally, make a fork of the main Dask repository, clone the fork:
git clone https://github.com/<your-github-username>/dask.git cd dask/docs
Install the packages in
Optionally create and activate a
conda environment first:
conda create -n daskdocs -c conda-forge python=3.8 conda activate daskdocs
Install the dependencies with
python -m pip install -r requirements-docs.txt
Then build the documentation with
The resulting HTML files end up in the
You can now make edits to rst files and run
make html again to update
the affected pages.
Dask CI Infrastructure¶
Dask uses Github Actions for Continuous Integration (CI) testing for each PR.
These CI builds will run the test suite across a variety of Python versions, operating
systems, and package dependency versions. Additionally, if a commit message
includes the phrase
test-upstream, then an additional CI build will be
triggered which uses the development versions of several dependencies
including: NumPy, pandas, fsspec, etc.
The CI workflows for Github Actions are defined in .github/workflows with additional scripts and metadata located in continuous_integration
Pull requests are also tested with a GPU enabled CI environment provided by
Unlike Github Actions, the CI environment for gpuCI is controlled with the
docker image. When making commits to the
dask-build-environment repo , a new image is built.
The docker image building process can be monitored
dask-build-environment has two separate Dockerfiles for Dask
and Distributed similarly, gpuCI will run for both Dask
For each PR, gpuCI will run all tests decorated with the pytest marker
@pytest.mark.gpu. This is configured in the gpuci folder .
Like Github Actions, gpuCI will not run when first time contributors to Dask or
Distributed submit PRs. In this case, the gpuCI bot will comment on the PR:
Can one of the admins verify this patch?
Dask Maintainers can then approve gpuCI builds for these PRs with following choices:
To only approve the PR contributor for the current PR, leave a comment which states
ok to test
To approve the current PR and all future PRs from the contributor, leave a comment which states
add to allowlist
For more information about gpuCI please consult the docs page