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Contributing to DataLad

Files organization

  • datalad/ is the main Python module where major development is happening, with major submodules being:
    • cmdline/ - helpers for accessing interface/ functionality from command line
    • crawler/ - functionality for crawling (online) resources and creating or updating datasets and collections based on the scraped/downloaded data
      • nodes/ processing elements which are used in the pipeline
      • pipelines/ pipelines generators, to produce pipelines to be ran
      • pipeline runner
    • customremotes/ - custom special remotes for annex provided by datalad
    • downloaders/ - support for accessing data from various sources (e.g. http, S3, XNAT) via a unified interface.
      • configs/ - specifications for known data providers and associated credentials
    • interface/ - high level interface functions which get exposed via command line (cmdline/) or Python (datalad.api).
    • tests/ - some unit- and regression- tests (more could be found under tests/ of corresponding submodules. See Tests)
      • provides convenience helpers used by unit-tests such as @with_tree, @serve_path_via_http and other decorators
    • ui/ - user-level interactions, such as messages about errors, warnings, progress reports, AND when supported by available frontend -- interactive dialogs
    • support/ - various support modules, e.g. for git/git-annex interfaces, constraints for the interface/, etc
  • benchmarks/ - asv benchmarks suite (see Benchmarking)
  • docs/ - yet to be heavily populated documentation
    • bash-completions - bash and zsh completion setup for datalad (just source it)
  • fixtures/ currently not under git, contains generated by vcr fixtures
  • tools/ contains helper utilities used during development, testing, and benchmarking of DataLad. Implemented in any most appropriate language (Python, bash, etc.)

How to contribute

The preferred way to contribute to the DataLad code base is to fork the main repository on GitHub. Here we outline the workflow used by the developers:

  1. Have a clone of our main project repository as origin remote in your git:

       git clone git://
  2. Fork the project repository: click on the 'Fork' button near the top of the page. This creates a copy of the code base under your account on the GitHub server.

  3. Add your forked clone as a remote to the local clone you already have on your local disk:

       git remote add gh-YourLogin
       git fetch gh-YourLogin

    To ease addition of other github repositories as remotes, here is a little bash function/script to add to your ~/.bashrc:

     ghremote () {
             git remote add gh-$login $url
             git fetch gh-$login

    thus you could simply run:


    to add the above gh-YourLogin remote. Additional handy aliases such as ghpr (to fetch existing pr from someone's remote) and ghsendpr could be found at yarikoptic's bash config file

  4. Create a branch (generally off the origin/master) to hold your changes:

       git checkout -b nf-my-feature

    and start making changes. Ideally, use a prefix signaling the purpose of the branch

    • nf- for new features
    • bf- for bug fixes
    • rf- for refactoring
    • doc- for documentation contributions (including in the code docstrings).
    • bm- for changes to benchmarks We recommend to not work in the master branch!
  5. Work on this copy on your computer using Git to do the version control. When you're done editing, do:

       git add modified_files
       git commit

    to record your changes in Git. Ideally, prefix your commit messages with the NF, BF, RF, DOC, BM similar to the branch name prefixes, but you could also use TST for commits concerned solely with tests, and BK to signal that the commit causes a breakage (e.g. of tests) at that point. Multiple entries could be listed joined with a + (e.g. rf+doc-). See git log for examples. If a commit closes an existing DataLad issue, then add to the end of the message (Closes #ISSUE_NUMER)

  6. Push to GitHub with:

       git push -u gh-YourLogin nf-my-feature

    Finally, go to the web page of your fork of the DataLad repo, and click 'Pull request' (PR) to send your changes to the maintainers for review. This will send an email to the committers. You can commit new changes to this branch and keep pushing to your remote -- github automagically adds them to your previously opened PR.

(If any of the above seems like magic to you, then look up the Git documentation on the web.)

Development environment

Although we now support Python 3 (>= 3.3), primarily we still use Python 2.7 and thus instructions below are for python 2.7 deployments. Replace python-{ with python{,3}-{ to also install dependencies for Python 3 (e.g., if you would like to develop and test through tox).

See for basic information about installation of datalad itself. On Debian-based systems we recommend to enable NeuroDebian since we use it to provide backports of recent fixed external modules we depend upon:

apt-get install -y -q git git-annex-standalone
apt-get install -y -q patool python-scrapy python-{appdirs,argcomplete,git,humanize,keyring,lxml,msgpack,mock,progressbar,requests,setuptools,six}

and additionally, for development we suggest to use tox and new versions of dependencies from pypy:

apt-get install -y -q python-{dev,httpretty,nose,pip,vcr,virtualenv} python-tox
# Some libraries which might be needed for installing via pip
apt-get install -y -q lib{ffi,ssl,curl4-openssl,xml2,xslt1}-dev

some of which you could also install from PyPi using pip (prior installation of those libraries listed above might be necessary)

pip install -r requirements-devel.txt

and you will need to install recent git-annex using appropriate for your OS means (for Debian/Ubuntu, once again, just use NeuroDebian).



We use NumPy standard for the description of parameters docstrings. If you are using PyCharm, set your project settings (Tools -> Python integrated tools -> Docstring format).

In addition, we follow the guidelines of Restructured Text with the additional features and treatments provided by Sphinx.

Additional Hints

Merge commits

For merge commits to have more informative description, add to your .git/config or ~/.gitconfig following section:

summary = true
log = true

and if conflicts occur, provide short summary on how they were resolved in "Conflicts" listing within the merge commit (see example).

Quality Assurance

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

  • All public methods should have informative docstrings with sample usage presented as doctests when appropriate.

  • All other tests pass when everything is rebuilt from scratch.

  • New code should be accompanied by tests.


datalad/tests contains tests for the core portion of the project, and more tests are provided under corresponding submodules in tests/ subdirectories to simplify re-running the tests concerning that portion of the codebase. To execute many tests, the codebase first needs to be "installed" in order to generate scripts for the entry points. For that, the recommended course of action is to use virtualenv, e.g.

virtualenv --system-site-packages venv-tests
source venv-tests/bin/activate
pip install -r requirements.txt
python develop

and then use that virtual environment to run the tests, via

python -m nose -s -v datalad

or similarly,

nosetests -s -v datalad

then to later deactivate the virtualenv just simply enter


Alternatively, or complimentary to that, you can use tox -- there is a tox.ini file which sets up a few virtual environments for testing locally, which you can later reuse like any other regular virtualenv for troubleshooting. Additionally, tools/testing/test_README_in_docker script can be used to establish a clean docker environment (based on any NeuroDebian-supported release of Debian or Ubuntu) with all dependencies listed in pre-installed.

CI setup

We are using Travis-CI and have buildbot setup which also exercises our tests battery for every PR and on the master. Note that buildbot runs tests only submitted by datalad developers, or if a PR acquires 'buildbot' label.

In case if you want to enter buildbot's environment

  1. Login to our development server (smaug)

  2. Find container ID associated with the environment you are interested in, e.g.

     docker ps | grep nd16.04
  3. Enter that docker container environment using

     docker exec -it <CONTAINER ID> /bin/bash
  4. Become buildbot user

     su - buildbot
  5. Activate corresponding virtualenv using

     source <VENV/bin/activate>

    e.g. source /home/buildbot/datalad-pr-docker-dl-nd15_04/build/venv-ci/bin/activate

And now you should be in the same environment as the very last tested PR. Note that the same path/venv is reused for all the PRs, so you might want first to check using git show under the build/ directory if it corresponds to the commit you are interested to troubleshoot.


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

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

        pip install nose coverage
        nosetests --with-coverage path/to/tests_for_package
  • We rely on to provide convenient view of code coverage. Installation of the codecov extension for Firefox/Iceweasel or Chromium is strongly advised, since it provides coverage annotation of pull requests.


We are not (yet) fully PEP8 compliant, so please use these tools as guidelines for your contributions, but not to PEP8 entire code base.

Sidenote: watch Raymond Hettinger - Beyond PEP 8

  • No pyflakes warnings, check with:

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

         pip install pep8
         pep8 path/to/
  • AutoPEP8 can help you fix some of the easy redundant errors:

         pip install autopep8
         autopep8 path/to/

Also, some team developers use PyCharm community edition which provides built-in PEP8 checker and handy tools such as smart splits/joins making it easier to maintain code following the PEP8 recommendations. NeuroDebian provides pycharm-community-sloppy package to ease pycharm installation even further.


We use asv to benchmark some core DataLad functionality. The benchmarks suite is located under benchmarks/, and periodically we publish results of running benchmarks on a dedicated host to . Those results are collected and available under the .asv/ submodule of this repository, so to get started

  • git submodule update --init .asv
  • pip install .[devel] or just pip install asv
  • asv machine - to configure asv for your host if you want to run benchmarks locally

And then you could use asv in multiple ways.

Quickly benchmark the working tree

  • asv run -E existing - benchmark using the existing python environment and just print out results (not stored anywhere). You can add -q to run each benchmark just once (thus less reliable estimates)
  • asv run -b api.supers.time_createadd_to_dataset -E existing would run that specific benchmark using the existing python environment

Note: --python=same (-E existing) seems to have restricted applicability, e.g. can't be used for a range of commits, so it can't be used with continuous.

Compare results for two commits from recorded runs

Use asv compare to compare results from different runs, which should be available under .asv/results/<machine>. In the example below we overcome a current limitation in asv compare that requires commits to be specified as hexshas:

> grp(){git rev-parse $1;}; asv compare -m hopa $(grp 0.9.x) $(grp master)

All benchmarks:

       before           after         ratio
     [b619eca4]       [7635f467]
-           1.87s            1.54s     0.82  api.supers.time_createadd
-           1.85s            1.56s     0.84  api.supers.time_createadd_to_dataset
-           5.57s            4.40s     0.79  api.supers.time_installr
          145±6ms          145±6ms     1.00  api.supers.time_ls
-           4.59s            2.17s     0.47  api.supers.time_remove
          427±1ms          434±8ms     1.02  api.testds.time_create_test_dataset1
-           4.10s            3.37s     0.82  api.testds.time_create_test_dataset2x2
      1.81±0.07ms      1.73±0.04ms     0.96  core.runner.time_echo
       2.30±0.2ms      2.04±0.03ms    ~0.89  core.runner.time_echo_gitrunner
+        420±10ms          535±3ms     1.27  core.startup.time_help_np
          111±6ms          107±3ms     0.96  core.startup.time_import
+         334±6ms          466±4ms     1.39  core.startup.time_import_api

Run and compare results for two commits

asv continuous could be used to first run benchmarks for the to-be-tested commits and then provide stats:

  • asv continuous 0.9.x master - would run and compare 0.9.x and master branches
  • asv continuous HEAD - would compare HEAD against HEAD^
  • asv continuous master HEAD - would compare HEAD against state of master
  • TODO: contineous -E existing


  • only significant changes will be reported
  • raw results from benchmarks are not stored (use --record-samples if desired)

Run and record benchmarks results (for later comparison etc)

Common options

  • -E to restrict to specific environment, e.g. -E virtualenv:2.7
  • -b could be used to specify specific benchmark(s)
  • -q to run benchmark just once for a quick assessment (results are not stored since too unreliable)

Easy Issues

A great way to start contributing to DataLad is to pick an item from the list of Easy issues in the issue tracker. Resolving these issues allows you to start contributing to the project without much prior knowledge. Your assistance in this area will be greatly appreciated by the more experienced developers as it helps free up their time to concentrate on other issues.

Various hints for developers

Useful tools

  • While performing IO/net heavy operations use dstat for quick logging of various health stats in a separate terminal window:

      dstat -c --top-cpu -d --top-bio --top-latency --net
  • To monitor speed of any data pipelining pv is really handy, just plug it in the middle of your pipe.

  • For remote debugging epdb could be used (avail in pip) by using import epdb; epdb.serve() in Python code and then connecting to it with python -c "import epdb; epdb.connect()".

  • We are using codecov which has extensions for the popular browsers (Firefox, Chrome) which annotates pull requests on github regarding changed coverage.

Useful Environment Variables

Refer datalad/ for information on how to add these environment variables to the config file and their naming convention

  • DATALAD_DATASETS_TOPURL: Used to point to an alternative location for /// dataset. If running tests preferred to be set to
  • DATALAD_LOG_LEVEL: Used for control the verbosity of logs printed to stdout while running datalad commands/debugging
  • DATALAD_LOG_CMD_OUTPUTS: Used to control either both stdout and stderr of external commands execution are logged in detail (at DEBUG level)
  • DATALAD_LOG_CMD_ENV: If contains a digit (e.g. 1), would log entire environment passed into the's popen call. Otherwise could be a comma separated list of environment variables to log
  • DATALAD_LOG_CMD_STDIN: Either to log stdin for the command
  • DATALAD_LOG_CMD_CWD: Either to log cwd where command to be executed
  • DATALAD_LOG_PID To instruct datalad to log PID of the process
  • DATALAD_LOG_TARGET Where to log: stderr (default), stdout, or another filename
  • DATALAD_LOG_TIMESTAMP: Used to add timestamp to datalad logs
  • DATALAD_LOG_TRACEBACK: Runs TraceBack function with collide set to True, if this flag is set to 'collide'. This replaces any common prefix between current traceback log and previous invocation with "..."
  • DATALAD_LOG_VMEM: Reports memory utilization (resident/virtual) at every log line, needs psutil module
  • DATALAD_EXC_STR_TBLIMIT: This flag is used by the datalad extract_tb function which extracts and formats stack-traces. It caps the number of lines to DATALAD_EXC_STR_TBLIMIT of pre-processed entries from traceback.
  • DATALAD_SEED: To seed Python's random RNG, which will also be used for generation of dataset UUIDs to make those random values reproducible. You might want also to set all the relevant git config variables like we do in one of the travis runs
  • DATALAD_TESTS_TEMP_KEEP: Function rmtemp will not remove temporary file/directory created for testing if this flag is set
  • DATALAD_TESTS_TEMP_DIR: Create a temporary directory at location specified by this flag. It is used by tests to create a temporary git directory while testing git annex archives etc
  • DATALAD_TESTS_NONETWORK: Skips network tests completely if this flag is set Examples include test for s3, git_repositories, openfmri etc
  • DATALAD_TESTS_SSH: Skips SSH tests if this flag is not set
  • DATALAD_TESTS_NOTEARDOWN: Does not execute teardown_package which cleans up temp files and directories created by tests if this flag is set
  • DATALAD_TESTS_USECASSETTE: Specifies the location of the file to record network transactions by the VCR module. Currently used by when testing custom special remotes
  • DATALAD_TESTS_OBSCURE_PREFIX: A string to prefix the most obscure (but supported by the filesystem test filename
  • DATALAD_TESTS_PROTOCOLREMOTE: Binary flag to specify whether to test protocol interactions of custom remote with annex
  • DATALAD_TESTS_RUNCMDLINE: Binary flag to specify if shell testing using shunit2 to be carried out
  • DATALAD_TESTS_TEMP_FS: Specify the temporary file system to use as loop device for testing DATALAD_TESTS_TEMP_DIR creation
  • DATALAD_TESTS_TEMP_FSSIZE: Specify the size of temporary file system to use as loop device for testing DATALAD_TESTS_TEMP_DIR creation
  • DATALAD_TESTS_NONLO: Specifies network interfaces to bring down/up for testing. Currently used by travis.
  • DATALAD_CMD_PROTOCOL: Specifies the protocol number used by the Runner to note shell command or python function call times and allows for dry runs. 'externals-time' for ExecutionTimeExternalsProtocol, 'time' for ExecutionTimeProtocol and 'null' for NullProtocol. Any new DATALAD_CMD_PROTOCOL has to implement
  • DATALAD_CMD_PROTOCOL_PREFIX: Sets a prefix to add before the command call times are noted by DATALAD_CMD_PROTOCOL.
  • DATALAD_USE_DEFAULT_GIT: Instructs to use git as available in current environment, and not the one which possibly comes with git-annex (default behavior).
  • DATALAD_ASSERT_NO_OPEN_FILES: Instructs internal tests for no open files under paths to be removed. If set to anything, it would log at ERROR level, and if set to "assert", it would raise AssertionError if any is

Changelog section

For the upcoming release use this template

0.10.3 (??? ??, 2018) -- will be better than ever

bet we will fix some bugs and make a world even a better place.

Major refactoring and deprecations

  • hopefully none



Enhancements and new features