A Recommender Framework in Python


Fork the source code, join the mailing lists, report bugs to the issue tracker or participate in the next coding sprint. Read More...


This project is maintained by Muriçoca Labs, and others.



This project is a community effort, and everyone is welcome to contribute.

The project is hosted on

Submitting a bug report

In case you experience issues using the package, do not hesitate to submit a ticket to the Bug Tracker.

You are also welcome to post there feature requests or links to pull-requests.

Retrieving the latest code

You can check the latest sources with the command:

git clone git://

or if you have write privileges:

git clone

Contributing code

How to contribute

The prefered way to contribute to Crab is to fork the main repository on github:

  1. Create an account on github if you don’t have one already.

  2. Fork the crab repo: click on the ‘Fork’ button, at the top, center of the page. This creates a copy of the code on the github server where you can work.

  3. Clone this copy to your local disk (you need the git program to do this):

    $ git clone
  4. Work on this copy, on your computer, using git to do the version control:

    $ git add modified_files
    $ git commit
    $ git push origin master

    and so on.

If your changes are not just trivial fixes, it is better to directly work in a branch with the name of the feature your are working on. In this case, replace step 4 by step 5:

  1. Create a branch to host your changes and publish it on your public repo:

    $ git checkout -b my-feature
    $ gid add modified_files
    $ git commit
    $ git push origin my-feature

When you are ready, and you have pushed your changes on your github repo, go the web page of the repo, and click on ‘Pull request’ to send us a pull request. This will send an email to the commiters, but might also send an email to the mailing list in order to get more visibility.

It is recommented to check that your contribution complies with the following rules before submitting a pull request:

  • Follow the coding-guidelines (see below).
  • All public methods should have informative docstrings with sample usage presented as doctests when appropriate.

You can also check for common programming errors with the following tools:

  • Code with a good unittest coverage (at least 80%), check with:

    $ pip install nose coverage
    $ nosetests --with-coverage path/to/tests_for_package
  • No pyflakes warnings, check with:

    $ pip install pyflakes
    $ pyflakes path/to/
  • No PEP8 warnings, check with:

    $ pip install pep8
    $ pep8 path/to/

Bonus points for contributions that include a performance analysis with a benchmark script and profiling output (please report on the mailing list or on the github wiki).


The current state of the crab code base is not compliant with all of those guidelines but we expect that enforcing those constraints on all new contributions will get the overall code base quality in the right direction.

EasyFix Issues

The best way to get your feet wet is to pick up an issue from the issue tracker that are labeled as EasyFix. This means that the knowledge needed to solve the issue is low, but still you are helping the project and letting more experienced developers concentrate on other issues.


We are glad to accept any sort of documentation: function docstrings, rst docs (like this one), tutorials, etc. Rst docs live in the source code repository, under directory doc/.

Further information about how to contribute will be explained here.


Sphinx version

While we do our best to have the documentation build under as many version of Sphinx as possible, the different versions tend to behave slightly differently. To get the best results, you should use version 1.0.

Developers web site

More information can be found at the developer’s wiki.

Other ways to contribute

Code is not the only way to contribute to this project. For instance, documentation is also a very important part of the project and ofter doesn’t get as much attention as it deserves. If you find a typo in the documentation, or have made improvements, don’t hesitate to send an email to the mailing list or a github pull request. Full documentation can be found under directory doc/.

It also helps us if you spread the word: reference it from your blog, articles, link to us from your website, or simply by saying “I use it”:

Coding guidelines

The following are some guidelines on how new code should be written. Of course, there are special cases and there will be exceptions to these rules. However, following these rules when submitting new code makes the review easier so new code can be integrated in less time.

Uniformly formatted code makes it easier to share code ownership. The Crab tries to follow closely the official Python guidelines detailed in PEP8 that details how code should be formatted, and indented. Please read it and follow it.

In addition, we add the following guidelines:

  • Use underscores to separate words in non class names: n_samples rather than nsamples.
  • Avoid multiple statements on one line. Prefer a line return after a control flow statement (if/for).
  • Use relative imports for references inside crab.
  • Please don’t use `import *` in any case. It is considered harmful by the official Python recommendations. It makes the code harder to read as the origin of symbols is no longer explicitly referenced, but most important, it prevents using a static analysis tool like pyflakes to automatically find bugs in Crab.
  • Use the numpy docstring standard in all your docstrings.

A good example of code that we like can be found here.

APIs of Crab objects

To have a uniform API, we try to have a common basic API for all the objects. In addition, to avoid the proliferation of framework code, we try to adopt simple conventions and limit to a minimum the number of methods an object has to implement.

We are still defining the standards of implementing for Crab.

Unresolved API issues

Some things are must still be decided:

  • Standard coding guidelines.
  • Refactoring of several methods and classes in early releases.

Working notes

For unresolved issues, TODOs, remarks on ongoing work, developers are adviced to maintain notes on the github wiki: