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Contributing

We appreciate all kinds of help, so thank you!

Contributor License Agreement

We'd love to accept your code! Before we can, we have to get a few legal requirements sorted out. By having you sign a Contributor License Agreement (CLA), we ensure that the community is free to use your contributions.

When you contribute to the Qiskit project with a new pull request, a bot will evaluate whether you have signed the CLA. If required, the bot will comment on the pull request, including a link to accept the agreement. The individual CLA document is available for review as a PDF.

If you work for a company that wants to allow you to contribute your work, then you'll need to sign a corporate CLA and email it to us at [email protected].

Contributing to the Project

You can contribute in many ways to this project.

Issue Reporting

This is a good point to start, when you find a problem please add it to the issue tracker. The ideal report should include the steps to reproduce it.

Doubts Solving

To help less advanced users is another wonderful way to start. You can help us close some opened issues. A ticket of this kind should be labeled as question.

Improvement Proposal

If you have an idea for a new feature, please open a ticket labeled as enhancement. If you could also add a piece of code with the idea or a partial implementation, that would be awesome.

Good First Contributions

You are welcome to contribute wherever in the code you want to, of course, but we recommend taking a look at the "Good First Contribution" label into the issues and pick one. We would love to mentor you!

Doc

Review the parts of the documentation regarding the new changes and update it if it's needed.

Pull Requests

We use GitHub pull requests to accept the contributions.

A friendly reminder! We'd love to have a previous discussion about the best way to implement the feature/bug you are contributing with. This is a good way to improve code quality in our beloved Qiskit Ignis! So remember to file a new issue before starting to code for a solution.

After having discussed the best way to land your changes into the codebase, you are ready to start coding. We have two options here:

  1. You think your implementation doesn't introduce a lot of code, right?. Ok, no problem, you are all set to create the PR once you have finished coding. We are waiting for it!
  2. Your implementation does introduce many things in the codebase. That sounds great! Thanks! In this case, you can start coding and create a PR with the word: [WIP] as a prefix of the description. This means "Work In Progress", and allows reviewers to make micro reviews from time to time without waiting for the big and final solution. Otherwise, it would make reviewing and coming changes pretty difficult to accomplish. The reviewer will remove the [WIP] prefix from the description once the PR is ready to merge.

Pull Request Checklist

When submitting a pull request and you feel it is ready for review, please double check that:

  • The code follows the code style of the project. For convenience, you can execute make style and make lint locally, which will print potential style warnings and fixes.
  • The documentation has been updated accordingly. In particular, if a function or class has been modified during the PR, please update the docstring accordingly.
  • Your contribution passes the existing tests, and if developing a new feature, that you have added new tests that cover those changes.
  • You add a new line to the CHANGELOG.md file, in the UNRELEASED section, with the title of your pull request and its identifier (for example, "Replace OldComponent with FluxCapacitor (#123)".

Commit Messages

Please follow the next rules for any commit message:

  • It should include a reference to the issue ID in the first line of the commit, and a brief description of the issue, so everybody knows what this ID actually refers to without wasting to much time on following the link to the issue.

  • It should provide enough information for a reviewer to understand the changes and their relation to the rest of the code.

A good example:

Issue #190: Short summary of the issue
* One of the important changes
* Another important change

Code

This section include some tips that will help you to push source code.

We recommend using Python virtual environments to cleanly separate Qiskit from other applications and improve your experience.

Setup with an Environment

The simplest way to use environments is by using Anaconda

conda create -y -n QiskitDevenv python=3
source activate QiskitDevenv

In order to execute the Ignis code, after cloning the Ignis GitHub repository on your machine, you need to have some libraries, which can be installed in this way:

cd qiskit-ignis
pip install -r requirements.txt
pip install -r requirements-dev.txt

To better contribute to Qiskit Ignis, we recommend that you clone the Qiskit Ignis repository and then install Qiskit Ignis from source. This will give you the ability to inspect and extend the latest version of the Ignis code more efficiently. The version of Qiskit Ignis in the repository's master branch is typically ahead of the version in the Python Package Index (PyPI) repository, and we strive to always keep Ignis in sync with the development versions of the Qiskit elements, each available in the master branch of the corresponding repository. Therefore, all the Qiskit elements and relevant components should be installed from source. This can be correctly achieved by first uninstalling them from the Python environment in which you have Qiskit (if they were previously installed), using the pip uninstall command for each of them. Next, after cloning the Qiskit Terra, Qiskit Aer, Qiskit IBMQ Provider and Qiskit Ignis repositories, you can install them from source in the same Python environment by issuing the following command repeatedly, from each of the root directories of those repository clones:

$ pip install -e .

exactly in the order specified above: Qiskit Terra, Qiskit Aer, Qiskit IBMQ Provider, and Qiskit Ignis. All the other dependencies will be installed automatically. This process may have to be repeated often as the master branch of Ignis is updated frequently.

Style guide

Please submit clean code and please make effort to follow existing conventions in order to keep it as readable as possible. We use the Pylint and PEP 8 style guide. To ensure your changes respect the style guidelines, run the next commands (all platforms):

$> cd out
out$> make lint
out$> make style

Documentation

The documentation source code for the project is located in the docs directory of the general Qiskit repository and automatically rendered on the Qiskit documentation Web site. The documentation for the Python SDK is auto-generated from Python docstrings using [Sphinx](http://www.sphinx-doc.org. Please follow Google's Python Style Guide for docstrings. A good example of the style can also be found with Sphinx's napolean converter documentation.

To generate the documentation, you need to invoke CMake first in order to generate all specific files for our current platform. See the instructions in the Terra repository for details on how to install and run CMake.

Development Cycle

Our development cycle is straightforward. Use the Projects board in Github for project management and use Milestones in the Issues board for releases. The features that we want to include in these releases will be tagged and discussed in the project boards. Whenever a new release is close to be launched, we'll announce it and detail what has changed since the latest version in our Release Notes and Changelog. The channels we'll use to announce new releases are still being discussed, but for now, you can follow us on Twitter!

Branch Model

There are two main branches in the repository:

  • master

    • This is the development branch.
    • Next release is going to be developed here. For example, if the current latest release version is r1.0.3, the master branch version will point to r1.1.0 (or r2.0.0).
    • You should expect this branch to be updated very frequently.
    • Even though we are always doing our best to not push code that breaks things, is more likely to eventually push code that breaks something... we will fix it ASAP, promise :).
    • This should not be considered as a stable branch to use in production environments.
    • The API of Qiskit could change without prior notice.

  • stable

    • This is our stable release branch.
    • It's always synchronized with the latest distributed package: as for now, the package you can download from pip.
    • The code in this branch is well tested and should be free of errors (unfortunately sometimes it's not).
    • This is a stable branch (as the name suggest), meaning that you can expect stable software ready for production environments.
    • All the tags from the release versions are created from this branch.

Release Cycle

From time to time, we will release brand new versions of Qiskit Terra. These are well-tested versions of the software.

When the time for a new release has come, we will:

  1. Merge the master branch with the stable branch.
  2. Create a new tag with the version number in the stable branch.
  3. Crate and distribute the pip package.
  4. Change the master version to the next release version.
  5. Announce the new version to the world!

The stable branch should only receive changes in the form of bug fixes, so the third version number (the maintenance number: [major].[minor].[maintenance]) will increase on every new change.

Stable Branch Policy

The stable branch is intended to be a safe source of fixes for high impact bugs and security issues which have been fixed on master since a release. When reviewing a stable branch PR we need to balance the risk of any given patch with the value that it will provide to users of the stable branch. Only a limited class of changes are appropriate for inclusion on the stable branch. A large, risky patch for a major issue might make sense. As might a trivial fix for a fairly obscure error handling case. A number of factors must be weighed when considering a change:

  • The risk of regression: even the tiniest changes carry some risk of breaking something and we really want to avoid regressions on the stable branch
  • The user visible benefit: are we fixing something that users might actually notice and, if so, how important is it?
  • How self-contained the fix is: if it fixes a significant issue but also refactors a lot of code, it’s probably worth thinking about what a less risky fix might look like
  • Whether the fix is already on master: a change must be a backport of a change already merged onto master, unless the change simply does not make sense on master.

Backporting procedure:

When backporting a patch from master to stable we want to keep a reference to the change on master. When you create the branch for the stable PR you can use:

$ git cherry-pick -x $master_commit_id

However, this only works for small self contained patches from master. If you need to backport a subset of a larger commit (from a squashed PR for example) from master this just need be done manually. This should be handled by adding::

Backported from: #master pr number

in these cases, so we can track the source of the change subset even if a strict cherry pick doesn't make sense.

If the patch you’re proposing will not cherry-pick cleanly, you can help by resolving the conflicts yourself and proposing the resulting patch. Please keep Conflicts lines in the commit message to help review of the stable patch.

Backport Tags

Bugs or PRs tagged with stable backport potential are bugs which apply to the stable release too and may be suitable for backporting once a fix lands in master. Once the backport has been proposed, the tag should be removed.

The PR against the stable branch should include [stable] in the title, as a sign that setting the target branch as stable was not a mistake. Also, reference to the PR number in master that you are porting.