Contributing

Yellowbrick is an open source project that is supported by a community who will gratefully and humbly accept any contributions you might make to the project. Large or small, any contribution makes a big difference; and if you’ve never contributed to an open source project before, we hope you will start with Yellowbrick!

Principally, Yellowbrick development is about the addition and creation of visualizers — objects that learn from data and create a visual representation of the data or model. Visualizers integrate with Scikit-Learn estimators, transformers, and pipelines for specific purposes and as a result, can be simple to build and deploy. The most common contribution is a new visualizer for a specific model or model family. We’ll discuss in detail how to build visualizers later.

Beyond creating visualizers, there are many ways to contribute:

  • Submit a bug report or feature request on GitHub Issues.
  • Contribute an Jupyter notebook to our examples gallery.
  • Assist us with user testing.
  • Add to the documentation or help with our website, scikit-yb.org
  • Write unit or integration tests for our project.
  • Answer questions on our issues, mailing list, Stack Overflow, and elsewhere.
  • Translate our documentation into another language.
  • Write a blog post, tweet, or share our project with others.
  • Teach someone how to use Yellowbrick.

As you can see, there are lots of ways to get involved and we would be very happy for you to join us! The only thing we ask is that you abide by the principles of openness, respect, and consideration of others as described in the Python Software Foundation Code of Conduct.

Getting Started on GitHub

Yellowbrick is hosted on GitHub at https://github.com/DistrictDataLabs/yellowbrick.

The typical workflow for a contributor to the codebase is as follows:

  1. Discover a bug or a feature by using Yellowbrick.
  2. Discuss with the core contributors by adding an issue.
  3. Assign yourself the task by pulling a card from our Waffle Kanban
  4. Fork the repository into your own GitHub account.
  5. Create a Pull Request first thing to connect with us about your task.
  6. Code the feature, write the tests and documentation, add your contribution.
  7. Review the code with core contributors who will guide you to a high quality submission.
  8. Merge your contribution into the Yellowbrick codebase.

Note

Please create a pull request as soon as possible, even before you’ve started coding. This will allow the core contributors to give you advice about where to add your code or utilities and discuss other style choices and implementation details as you go. Don’t wait!

We believe that contribution is collaboration and therefore emphasize communication throughout the open source process. We rely heavily on GitHub’s social coding tools to allow us to do this.

Forking the Repository

The first step is to fork the repository into your own account. This will create a copy of the codebase that you can edit and write to. Do so by clicking the “fork” button in the upper right corner of the Yellowbrick GitHub page.

Once forked, use the following steps to get your development environment set up on your computer:

  1. Clone the repository.

    After clicking the fork button, you should be redirected to the GitHub page of the repository in your user account. You can then clone a copy of the code to your local machine.:

    $ git clone https://github.com/[YOURUSERNAME]/yellowbrick
    $ cd yellowbrick
    
  2. Create a virtual environment.

    Yellowbrick developers typically use virtualenv (and virtualenvwrapper), pyenv or conda envs in order to manage their Python version and dependencies. Using the virtual environment tool of your choice, create one for Yellowbrick. Here’s how with virtualenv:

    $ virtualenv venv
    
  3. Install dependencies.

    Yellowbrick’s dependencies are in the requirements.txt document at the root of the repository. Open this file and uncomment the dependencies that are for development only. Then install the dependencies with pip:

    $ pip install -r requirements.txt
    

    Note that there may be other dependencies required for development and testing; you can simply install them with pip.

  4. Switch to the develop branch.

    The Yellowbrick repository has a develop branch that is the primary working branch for contributions. It is probably already the branch you’re on, but you can make sure and switch to it as follows:

    $ git fetch
    $ git checkout develop
    

At this point you’re ready to get started writing code. If you’re going to take on a specific task, we’d strongly encourage you to check out the issue on Waffle and create a pull request before you start coding to better foster communication with other contributors.

The next section is about managing GitHub branches for contributions, but if you’re ready jump straight to Developing Visualizers!

Branching Convention

The Yellowbrick repository is set up in a typical production/release/development cycle as described in “A Successful Git Branching Model.” The primary working branch is the develop branch. This should be the branch that you are working on and from, since this has all the latest code. The master branch contains the latest stable version and release, which is pushed to PyPI. No one but core contributors will generally push to master.

Note

All pull requests should be into the yellowbrick/develop branch from your forked repository.

You can work directly in your fork and create a pull request from your fork’s develop branch into ours. We also recommend setting up an upstream remote so that you can easily pull the latest development changes from the main Yellowbrick repository (see configuring a remote for a fork). You can do that as follows:

$ git remote add upstream https://github.com/DistrictDataLabs/yellowbrick.git
$ git remote -v
origin    https://github.com/YOUR_USERNAME/YOUR_FORK.git (fetch)
origin    https://github.com/YOUR_USERNAME/YOUR_FORK.git (push)
upstream  https://github.com/DistrictDataLabs/yellowbrick.git (fetch)
upstream  https://github.com/DistrictDataLabs/yellowbrick.git (push)

When you’re ready, request a code review for your pull request. Then, when reviewed and approved, you can merge your fork into our main branch. Make sure to use the “Squash and Merge” option in order to create a Git history that is understandable.

Note

When merging a pull request, use the “squash and merge” option.

Core contributors have write access to the repository. In order to reduce the number of merges (and merge conflicts) we recommend that you utilize a feature branch off of develop to do intermediate work in:

$ git checkout -b feature-myfeature develop

Once you are done working (and everything is tested) merge your feature into develop.:

$ git checkout develop
$ git merge --no-ff feature-myfeature
$ git branch -d feature-myfeature
$ git push origin develop

Head back to Waffle and checkout another issue!

Releases

When ready to create a new release we branch off of develop as follows:

$ git checkout -b release-x.x

This creates a release branch for version x.x. At this point do the version bump by modifying version.py and the test version in tests/__init__.py. Make sure all tests pass for the release and that the documentation is up to date. There may be style changes or deployment options that have to be done at this phase in the release branch. At this phase you’ll also modify the changelog with the features and changes in the release.

Once the release is ready for prime-time, merge into master:

$ git checkout master
$ git merge --no-ff --no-edit release-x.x

Tag the release in GitHub:

$ git tag -a vx.x
$ git push origin vx.x

You’ll have to go to the release page to edit the release with similar information as added to the changelog. Once done, push the release to PyPI:

$ make build
$ make deploy

Check that the PyPI page is updated with the correct version and that pip install -U yellowbrick updates the version and works correctly. Also check the documentation on PyHosted, ReadTheDocs, and on our website to make sure that it was correctly updated. Finally merge the release into develop and clean up:

$ git checkout develop
$ git merge --no-ff --no-edit release-x.x
$ git branch -d release-x.x

Hotfixes and minor releases also follow a similar pattern; the goal is to effectively get new code to users as soon as possible!

Developing Visualizers

In this section, we’ll discuss the basics of developing visualizers. This of course is a big topic, but hopefully these simple tips and tricks will help make sense. First thing though, check out this presentation that we put together on yellowbrick development, it discusses the expected user workflow, our integration with Scikit-Learn, our plans and roadmap, etc:

One thing that is necessary is a good understanding of Scikit-Learn and Matplotlib. Because our API is intended to integrate with Scikit-Learn, a good start is to review “APIs of Scikit-Learn objects” and “rolling your own estimator”. In terms of matplotlib, check out Nicolas P. Rougier’s Matplotlib tutorial.

Visualizer API

There are two basic types of Visualizers:

  • Feature Visualizers are high dimensional data visualizations that are essentially transformers.
  • Score Visualizers wrap a Scikit-Learn regressor, classifier, or clusterer and visualize the behavior or performance of the model on test data.

These two basic types of visualizers map well to the two basic objects in Scikit-Learn:

  • Transformers take input data and return a new data set.
  • Estimators are fit to training data and can make predictions.

The Scikit-Learn API is object oriented, and estimators and transformers are initialized with parameters by instantiating their class. Hyperparameters can also be set using the set_attrs() method and retrieved with the corresponding get_attrs() method. All Scikit-Learn estimators have a fit(X, y=None) method that accepts a two dimensional data array, X, and optionally a vector y of target values. The fit() method trains the estimator, making it ready to transform data or make predictions. Transformers have an associated transform(X) method that returns a new dataset, Xprime and models have a predict(X) method that returns a vector of predictions, yhat. Models also have a score(X, y) method that evaluate the performance of the model.

Visualizers interact with Scikit-Learn objects by intersecting with them at the methods defined above. Specifically, visualizers perform actions related to fit(), transform(), predict(), and score() then call a draw() method which initializes the underlying figure associated with the visualizer. The user calls the visualizer’s poof() method, which in turn calls a finalize() method on the visualizer to draw legends, titles, etc. and then poof() renders the figure. The Visualizer API is therefore:

  • draw(): add visual elements to the underlying axes object
  • finalize(): prepare the figure for rendering, adding final touches such as legends, titles, axis labels, etc.
  • poof(): render the figure for the user (or saves it to disk).

Creating a visualizer means defining a class that extends Visualizer or one of its subclasses, then implementing several of the methods described above. A barebones implementation is as follows:

import matplotlib.pyplot as plot

from yellowbrick.base import Visualizer

class MyVisualizer(Visualizer):

    def __init__(self, ax=None, **kwargs):
        super(MyVisualizer, self).__init__(ax, **kwargs)

    def fit(self, X, y=None):
        self.draw(X)
        return self

    def draw(self, X):
        if self.ax is None:
            self.ax = self.gca()

        self.ax.plot(X)

    def finalize(self):
        self.set_title("My Visualizer")

This simple visualizer simply draws a line graph for some input dataset X, intersecting with the Scikit-Learn API at the fit() method. A user would use this visualizer in the typical style:

visualizer = MyVisualizer()
visualizer.fit(X)
visualizer.poof()

Score visualizers work on the same principle but accept an additional required model argument. Score visualizers wrap the model (which can be either instantiated or uninstantiated) and then pass through all attributes and methods through to the underlying model, drawing where necessary.

Testing

The test package mirrors the yellowbrick package in structure and also contains several helper methods and base functionality. To add a test to your visualizer, find the corresponding file to add the test case, or create a new test file in the same place you added your code.

Visual tests are notoriously difficult to create — how do you test a visualization or figure? Moreover, testing Scikit-Learn models with real data can consume a lot of memory. Therefore the primary test you should create is simply to test your visualizer from end to end and make sure that no exceptions occur. To assist with this, we have two primary helpers, VisualTestCase and DatasetMixin. Create your unittest as follows:

from tests.base import VisualTestCase
from tests.dataset import DatasetMixin

class MyVisualizerTests(VisualTestCase, DatasetMixin):

    def test_my_visualizer(self):
        """
        Test MyVisualizer on a real dataset
        """
        # Load the data from the fixture
        dataset = self.load_data('occupancy')

        # Get the data
        X = dataset[[
            "temperature", "relative_humidity", "light", "C02", "humidity"
        ]]
        y = dataset['occupancy'].astype(int)

        try:
            visualizer = MyVisualizer()
            visualizer.fit(X)
            visualizer.poof()
        except Exception as e:
            self.fail("my visualizer didn't work")

Tests can be run as follows:

$ make test

The Makefile uses the nosetest runner and testing suite as well as the coverage library, so make sure you have those dependencies installed! The DatasetMixin also requires requests.py to fetch data from our Amazon S3 account.

Documentation

The initial documentation for your visualizer will be a well structured docstring. Yellowbrick uses Sphinx to build documentation, therefore docstrings should be written in reStructuredText in numpydoc format (similar to Scikit-Learn). The primary location of your docstring should be right under the class definition, here is an example:

class MyVisualizer(Visualizer):
    """
    This initial section should describe the visualizer and what
    it's about, including how to use it. Take as many paragraphs
    as needed to get as much detail as possible.

    In the next section describe the parameters to __init__.

    Parameters
    ----------

    model : a Scikit-Learn regressor
        Should be an instance of a regressor, and specifically one whose name
        ends with "CV" otherwise a will raise a YellowbrickTypeError exception
        on instantiation. To use non-CV regressors see:
        ``ManualAlphaSelection``.

    ax : matplotlib Axes, default: None
        The axes to plot the figure on. If None is passed in the current axes
        will be used (or generated if required).

    kwargs : dict
        Keyword arguments that are passed to the base class and may influence
        the visualization as defined in other Visualizers.

    Examples
    --------

    >>> model = MyVisualizer()
    >>> model.fit(X)
    >>> model.poof()

    Notes
    -----

    In the notes section specify any gotchas or other info.
    """

You should also add your example to the examples directory of the documentation when you have the chance, as well as create a demonstration in a notebook in the examples directory of the repository.