source/developer/contributing.rst

Contributing to Numba
=====================

We welcome people who want to make contributions to Numba, big or small!
Even simple documentation improvements are encouraged.  If you have
questions, don't hesitate to ask them (see below).


Communication
-------------

Real-time Chat
''''''''''''''

Numba uses Gitter for public real-time chat.  To help improve the
signal-to-noise ratio, we have two channels:

* `numba/numba <https://gitter.im/numba/numba>`_: General Numba discussion,
  questions, and debugging help.
* `numba/numba-dev <https://gitter.im/numba/numba-dev>`_: Discussion of PRs,
  planning, release coordination, etc.

Both channels are public, but we may ask that discussions on numba-dev move to
the numba channel.  This is simply to ensure that numba-dev is easy for core
developers to keep up with.

Note that the Github issue tracker is the best place to report bugs.  Bug
reports in chat are difficult to track and likely to be lost.

Forum
.....

Numba uses Discourse as a forum for longer running threads such as design
discussions and roadmap planning. There are various categories available and it
can be reached at: `numba.discourse.group <https://numba.discourse.group/>`_.

Mailing-list
''''''''''''

We have a public mailing-list that you can e-mail at numba-users@anaconda.com.
You can subscribe and read the archives on
`Google Groups <https://groups.google.com/a/continuum.io/forum/#!forum/numba-users>`_.

Weekly Meetings
'''''''''''''''

The core Numba developers have a weekly video conference to discuss roadmap,
feature planning, and outstanding issues.  These meetings are invite only, but
minutes will be taken and will be posted to the
`Numba wiki <https://github.com/numba/numba/wiki/Meeting-Minutes>`_.

.. _report-numba-bugs:

Bug tracker
''''''''''''

We use the `Github issue tracker <https://github.com/numba/numba/issues>`_
to track both bug reports and feature requests.  If you report an issue,
please include specifics:

* what you are trying to do;
* which operating system you have and which version of Numba you are running;
* how Numba is misbehaving, e.g. the full error traceback, or the unexpected
  results you are getting;
* as far as possible, a code snippet that allows full reproduction of your
  problem.

Getting set up
--------------

If you want to contribute, we recommend you fork our `Github repository
<https://github.com/numba/numba>`_, then create a branch representing
your work.  When your work is ready, you should submit it as a pull
request from the Github interface.

If you want, you can submit a pull request even when you haven't finished
working.  This can be useful to gather feedback, or to stress your changes
against the :ref:`continuous integration <travis_ci>` platform.  In this
case, please prepend ``[WIP]`` to your pull request's title.

.. _buildenv:

Build environment
'''''''''''''''''

Numba has a number of dependencies (mostly `NumPy <http://www.numpy.org/>`_
and `llvmlite <https://github.com/numba/llvmlite>`_) with non-trivial build
instructions.  Unless you want to build those dependencies yourself, we
recommend you use `conda <http://conda.pydata.org/miniconda.html>`_ to
create a dedicated development environment and install precompiled versions
of those dependencies there.

First add the Anaconda Cloud ``numba`` channel so as to get development builds
of the llvmlite library::

   $ conda config --add channels numba

Then create an environment with the right dependencies::

   $ conda create -n numbaenv python=3.6 llvmlite numpy scipy jinja2 cffi

.. note::
   This installs an environment based on Python 3.6, but you can of course
   choose another version supported by Numba.  To test additional features,
   you may also need to install ``tbb`` and/or ``llvm-openmp`` and
   ``intel-openmp``.

To activate the environment for the current shell session::

   $ conda activate numbaenv

.. note::
   These instructions are for a standard Linux shell.  You may need to
   adapt them for other platforms.

Once the environment is activated, you have a dedicated Python with the
required dependencies::

    $ python
    Python 3.6.6 |Anaconda, Inc.| (default, Jun 28 2018, 11:07:29)
    [GCC 4.2.1 Compatible Clang 4.0.1 (tags/RELEASE_401/final)] on darwin
    Type "help", "copyright", "credits" or "license" for more information.
    >>> import llvmlite
    >>> llvmlite.__version__
    '0.24.0'


Building Numba
''''''''''''''

For a convenient development workflow, we recommend you build Numba inside
its source checkout::

   $ git clone git://github.com/numba/numba.git
   $ cd numba
   $ python setup.py build_ext --inplace

This assumes you have a working C compiler and runtime on your development
system.  You will have to run this command again whenever you modify
C files inside the Numba source tree.

Running tests
'''''''''''''

Numba is validated using a test suite comprised of various kind of tests
(unit tests, functional tests). The test suite is written using the
standard :py:mod:`unittest` framework.

The tests can be executed via ``python -m numba.runtests``.  If you are
running Numba from a source checkout, you can type ``./runtests.py``
as a shortcut.  Various options are supported to influence test running
and reporting.  Pass ``-h`` or ``--help`` to get a glimpse at those options.
Examples:

* to list all available tests::

    $ python -m numba.runtests -l

* to list tests from a specific (sub-)suite::

    $ python -m numba.runtests -l numba.tests.test_usecases

* to run those tests::

    $ python -m numba.runtests numba.tests.test_usecases

* to run all tests in parallel, using multiple sub-processes::

    $ python -m numba.runtests -m

* For a detailed list of all options::

    $ python -m numba.runtests -h

The numba test suite can take a long time to complete.  When you want to avoid
the long wait,  it is useful to focus on the failing tests first with the
following test runner options:

* The ``--failed-first`` option is added to capture the list of failed tests
  and to re-execute them first::

    $ python -m numba.runtests --failed-first -m -v -b

* The ``--last-failed`` option is used with ``--failed-first`` to execute
  the previously failed tests only::

    $ python -m numba.runtests --last-failed -m -v -b

When debugging, it is useful to turn on logging.  Numba logs using the
standard ``logging`` module.  One can use the standard ways (i.e.
``logging.basicConfig``) to configure the logging behavior.  To enable logging
in the test runner, there is a ``--log`` flag for convenience::

    $ python -m numba.runtests --log


Development rules
-----------------

Code reviews
''''''''''''

Any non-trivial change should go through a code review by one or several of
the core developers.  The recommended process is to submit a pull request
on github.

A code review should try to assess the following criteria:

* general design and correctness
* code structure and maintainability
* coding conventions
* docstrings, comments
* test coverage

Coding conventions
''''''''''''''''''

All Python code should follow :pep:`8`.  Our C code doesn't have a
well-defined coding style (would it be nice to follow :pep:`7`?).
Code and documentation should generally fit within 80 columns, for
maximum readability with all existing tools (such as code review UIs).

Numba uses `Flake8 <http://flake8.pycqa.org/en/latest/>`_ to ensure a consistent
Python code format throughout the project. ``flake8`` can be installed
with ``pip`` or ``conda`` and then run from the root of the Numba repository::

    flake8 numba

Optionally, you may wish to setup `pre-commit hooks <https://pre-commit.com/>`_
to automatically run ``flake8`` when you make a git commit. This can be
done by installing ``pre-commit``::

    pip install pre-commit

and then running::

    pre-commit install

from the root of the Numba repository. Now ``flake8`` will be run each time
you commit changes. You can skip this check with ``git commit --no-verify``.

Numba has started the process of using `type hints <https://www.python.org/dev/peps/pep-0484/>`_ in its code base. This
will be a gradual process of extending the number of files that use type hints, as well as going from voluntary to
mandatory type hints for new features. `Mypy <http://mypy-lang.org/>`_ is used for automated static checking.

At the moment, only certain files are checked by mypy. The list can be found in ``mypy.ini``. When making changes to
those files, it is necessary to add the required type hints such that mypy tests will pass. Only in exceptional
circumstances should ``type: ignore`` comments be used.

If you are contributing a new feature, we encourage you to use type hints, even if the file is not currently in the
checklist. If you want to contribute type hints to enable a new file to be in the checklist, please add the file to the
``files`` variable in ``mypy.ini``, and decide what level of compliance you are targetting. Level 3 is basic static
checks, while levels 2 and 1 represent stricter checking. The levels are described in details in ``mypy.ini``.

There is potential for confusion between the Numba module ``typing`` and Python built-in module ``typing`` used for type
hints, as well as between Numba types---such as ``Dict`` or ``Literal``---and ``typing`` types of the same name.
To mitigate the risk of confusion we use a naming convention by which objects of the built-in ``typing`` module are
imported with an ``pt`` prefix. For example, ``typing.Dict`` is imported as ``from typing import Dict as ptDict``.

Stability
'''''''''

The repository's ``master`` branch is expected to be stable at all times.
This translates into the fact that the test suite passes without errors
on all supported platforms (see below).  This also means that a pull request
also needs to pass the test suite before it is merged in.

.. _travis_ci:

Platform support
''''''''''''''''

Every commit to the master branch is automatically tested on all of the
platforms Numba supports.  This includes ARMv7, ARMv8, POWER8, as well as both
AMD and NVIDIA GPUs.  The build system however is internal to Anaconda, so we
also use `Travis CI <https://travis-ci.org/numba/numba>`_ and
`Azure <https://dev.azure.com/numba/numba/_build>`_ to provide public continuous
integration information for as many combinations as can be supported by the
service.  Travis CI automatically tests all pull requests on OS X and Linux, as
well as a sampling of different Python and NumPy versions, Azure does the same
but also includes Windows.  If you see problems on platforms you are unfamiliar
with, feel free to ask for help in your pull request.  The Numba core developers
can help diagnose cross-platform compatibility issues.


Documentation
-------------

The Numba documentation is split over two repositories:

* This documentation is in the ``docs`` directory inside the
  `Numba repository <https://github.com/numba/numba>`_.

* The `Numba homepage <http://numba.pydata.org>`_ has its sources in a
  separate repository at https://github.com/numba/numba-webpage


Main documentation
''''''''''''''''''

This documentation is under the ``docs`` directory of the `Numba repository`_.
It is built with `Sphinx <http://sphinx-doc.org/>`_ and
`numpydoc <https://numpydoc.readthedocs.io/>`_, which are available using
conda or pip; i.e. ``conda install sphinx numpydoc``.

To build the documentation, you need the bootstrap theme::

   $ pip install sphinx_bootstrap_theme

You can edit the source files under ``docs/source/``, after which you can
build and check the documentation::

   $ make html
   $ open _build/html/index.html

Core developers can upload this documentation to the Numba website
at http://numba.pydata.org by using the ``gh-pages.py`` script under ``docs``::

   $ python gh-pages.py version  # version can be 'dev' or '0.16' etc

then verify the repository under the ``gh-pages`` directory and use
``git push``.

Web site homepage
'''''''''''''''''

The Numba homepage on http://numba.pydata.org can be fetched from here:
https://github.com/numba/numba-webpage

After pushing documentation to a new version, core developers will want to
update the website.  Some notable files:

* ``index.rst``       # Update main page
* ``_templates/sidebar_versions.html``    # Update sidebar links
* ``doc.rst``         # Update after adding a new version for numba docs
* ``download.rst``    # Updata after uploading new numba version to pypi

After updating run::

   $ make html

and check out ``_build/html/index.html``.  To push updates to the Web site::

   $ python _scripts/gh-pages.py

then verify the repository under the ``gh-pages`` directory.  Make sure the
``CNAME`` file is present and contains a single line for ``numba.pydata.org``.
Finally, use ``git push`` to update the website.