Organize Your Work in Satellite Packages

This tutorial explains how to use zc.buildout to build complete Python-based working environments (a.k.a satellite packages) which are isolated from your current python installation. By following this recipe you will be able to:

• Create a basic working environment using either a stock Bob installation or your own compiled (and possibly uninstalled) version of Bob;
• Install additional python packages to augment your virtual work environment capabilities - e.g., to include a new python package for a specific purpose covering functionality that does not necessarily exists in Bob;
• Distribute your work to others in a clean and organized manner.

The advantaged of using zc.buildout is that it does not require administrator privileges for setting up all of the above. Furthermore, you will be able to create isolated environments for each project you have, individually. This is a great way, for example, to release code for laboratory exercises or for a particular publication that depends on Bob.

Note

The core of our strategy is based on standard tools for defining and deploying Python packages. If you are not familiar with Python’s setuptools, distutils or PyPI, it can be beneficial to learn about those before you start. Python Setuptools and Distutils are mechanisms to define and distribute python code in a packaged format, optionally through PyPI, a web-based Python package index and distribution portal.

Buildout is a tool to deploy Python packages locally, automatically setting up and isolating your environment.

Anatomy of a buildout Python package

The best way to create your package is to download a skeleton from the Idiap github website and build on it, modifying what you need. Fire-up a shell window and than do this:

$ git clone --depth=1 https://github.com/idiap/bob.project.example.git
$ cd bob.project.example
$ rm -rf .git #this is optional - you won't need the .git directory

We now recommend you read the file readme.rst situated at the root of the just downloaded material. It contains important information on other functionality such as document generation and unit testing, which will not be covered on this introductory material.

The anatomy of a minimal package should look like the following:

.
|-- MANIFEST.in   # describes which files should be installed, besides the python ones
|-- README.rst    # a descriptive explanation of the package contents, in restructured-text format
|-- bootstrap.py  # stock script downloaded from http://svn.zope.org/*checkout*/zc.buildout/trunk/bootstrap/bootstrap.py
|-- buildout.cfg  # buildout configuration to create a local working environment for this package
|-- setup.py      # installation + requirements for this particular package
|-- docs          # documentation directory
|   |-- conf.py   # Sphinx configuration
|   |-- index.rst # Documentation starting point for Sphinx
|-- xbob          # python package (a.k.a. "the code")
|   |-- example
|   |   |-- script
|   |   |   |-- __init__.py
|   |   |   |-- version.py
|   |   |-- __init__.py
|   |   |-- test.py
|   |-- __init__.py

Our example that you just downloaded contains these files and a few extra ones useful for this tutorial. Inspect the package so you are aware of its contents. All files are in text format and should be heavily commented. The most important file that requires your attention is setup.py. This file contains the basic information for the Python package you will be creating and defines scripts it creates and dependencies it requires for execution. To customize the package to your needs, you will need to edit this file and modify it accordingly. Before doing so, it is suggested you go through all of this tutorial so you are familiar with the whole environment. The example package, as it is distributed, contains a fully working example.

In the remaining of this text, we start by explaining the simplest use case: when you have Bob centrally installed so you can import it on your Python prompt without further setup. If that is not the case, you will need to follow the supplementary instructions down below so to make buildout aware of Bob‘s installation location. Both are easy, but let’s start with the simplest one.

You have Bob centrally installed

This is the typical case when you have installed one of our pre-packaged versions of Bob or you have setup your account or machine so that Bob is automatically found when you start your Python prompt. To check if you satisfy that condition, just fire up Python and try to import bob:

$ python
>>> import bob

If that works, setting-up your work environment is no different than what is described on the buildout website. Here is a screencast by the author of buildout that explains that process in details.

The package you cloned above contains all elements to get you started. It defines a single library inside called example, which declares a simple script, called version.py that prints out the version of Bob. When you clone the package, you will not find any executable as buildout needs to check all dependencies and install missing ones before you can execute anything. Here is how to go from nothing to everything:

$ python bootstrap.py
  Downloading http://pypi.python.org/packages/2.6/s/setuptools/setuptools-0.6c11-py2.6.egg
  Creating directory '/Users/andre/Projects/bob.project.example/bin'.
  Creating directory '/Users/andre/Projects/bob.project.example/parts'.
  Creating directory '/Users/andre/Projects/bob.project.example/eggs'.
  Creating directory '/Users/andre/Projects/bob.project.example/develop-eggs'.
  Getting distribution for 'setuptools'.
  Got setuptools 0.6c12dev-r88846.
  Generated script '/Users/andre/Projects/bob.project.example/bin/buildout'.
$ ./bin/buildout
  Develop: '/Users/andre/Projects/bob.project.example/.'
  Installing python.
  Generated script '/Users/andre/Projects/bob.project.example/bin/version.py'.
  Generated interpreter '/Users/andre/Projects/bob.project.example/bin/python'.
  ...

Note

The python shell used in the first line of the previous command set determines the python interpreter that will be used for all scripts developed inside this package. Because this package makes use of Bob, you must make sure that the bootstrap.py script is called with the same interpreter used to build Bob, or unexpected problems might occur.

If Bob is installed by the administrator of your system, it is safe to consider it uses the default python interpreter. In this case, the above 2 command lines should work as expected.

You should now be able to execute ./bin/version.py:

$ ./bin/version.py
  The installed version of Bob is '1.0.2'

Everything is now setup for you to continue the development of this package. Modify all required files to setup your own package name, description and dependencies. Start adding files to your library (or libraries) and, if you wish, make this package available in a place with public access to make your research public. We recommend using Github. Optionally, drop-us a message talking about the availability of this package so we can add it to the growing list of available software.

Bob is installed somewhere else

This is the typical case when you compile Bob from scratch, yourself, and decided not to install it formally in some automatically scanned location (like /usr). For example, you may want to test a new version of Bob with your setup or check which API changes will affect your released code. In such cases, you will need to tell buildout what is the base build directory or installation prefix for Bob.

To do that, alter the section external in buildout.cfg and replace or add directories (one per line) in which buildout will search for Bob python eggs (compiled and distributed with Bob builds). Bob Python Eggs are located inside the lib directory at the build or installation prefixes. Here are some examples:

[external]
recipe = xbob.buildout:external
egg-directories = /my/bob/build/directory/lib

The xbob.buildout:external buildout recipe will search recursively all directories given in the egg-directories entry and setup all Bob python eggs found in those. For more information and options for this recipe, refer to its manual <http://pypi.python.org/pypi/xbob.buildout/>.

Document Generation and Unit Testing

If you intend to distribute your newly created package, please consider carefully documenting and creating unit tests for your package. Documentation is a great starting point for users and unit tests can be used to check funcionality in unexpected circumstances such as variations in package versions.

Documentation

To write documentation, use the Sphinx Document Generator. A template has been setup for you under the docs directory. Get familiar with Sphinx and then unleash the writer in you.

Once you have edited both docs/conf.py and docs/index.rst you can run the document generator executing ./bin/sphinx. The system is setup to generate output at the sphinx directory.

For more details and tweaking hints checkout the manual for xbob.buildout.

Note

If the code you are distributing corresponds to the work described in a publication, don’t forget to mention it in your README.rst file.

Unit Tests

Writing unit tests is an important asset on code that needs to run in different platforms and a great way to make sure all is OK. We have setup a template for tests under example/test.py. Tests are setup in buildout` using the recipe xbob.buildout:nose` <http://pypi.python.org/pypi/xbob.buildout/>`_. A script called ./bin/tests.py will be created which can run anything that resembles a test on the example package.

Note

Packages are sometimes distributed so that can be useful to other packages. If you plan to distribute your package, make sure to declare a bob.test entry-point on your setup.py. If you do that, others may be able to run your tests from their package. An example script that could do that is installed in our bob.db.aggregator package and looks like this:

# execute all declared bob.test entries
import pkg_resources
for i, ep in enumerate(pkg_resources.iter_entry_points('bob.test')):
  cls = ep.load()
  exec('Test%d = cls' % i)

Creating Database Satellite Packages

Database satellite packages are special satellite packages that can hook-in Bob‘s database manager bob_dbmanage.py. Except for this detail, they should look exactly like a normal package.

To allow the database to be hooked to the bob_dbmanage.py you must implement a non-virtual python class that inherits from bob.db.driver.Interface. Your concrete implementation should then be described at the setup.py file with a special bob.db entry point:

# bob database declaration
'bob.db': [
  'replay = xbob.db.replay.driver:Interface',
  ],

At present, there is no formal design guide for databases. Nevertheless, it is considered a good practice to follow the design of currently existing database packages. This should ease migration in case of future changes.

Python Package Namespace

We like to make use of namespaces to define combined sets of functionality that go well together. Python package namespaces are explained in details here together with implementation details. Two basic namespaces are available when you are operating with Bob or add-ons, such as database access APIs (shipped separately): the bob namespace is reserved for utilities built and shiped with Bob. The namespace xbob (as for external Bob packages) should be used for all other applications that are meant to be distributed and augment Bob‘s features.

The example package you downloaded creates package inside the xbob namespace called example. Examine this example in details and understand how to distributed namespace’d packages in the URL above.

In particular, if you are creating a database access API, please consider putting all of your package contents inside the namespace xbob.db.<package>, therefore declaring two namespaces: xbob and xbob.db. All standard database access APIs follow this strategy. Just look at our currently existing database packages for examples.

Distributing Your Work

To distribute a package, we recommend you use PyPI. The The Hitchhiker’s Guide to Packaging contains details and good examples on how to achieve this.

Version Numbering Scheme

We recommend you follow Bob‘s version numbering scheme using a 3-tier string: M.m.p. The value of M is a number starting at 1. This number is changed in case of a major release that brings new APIs and concepts to the table. The value of m is a number starting at 0 (zero). Every time a new API is available (but no conceptual modifications are done to the platform) that number is increased. Finally, the value of p represents the patch level, starting at 0 (zero). Every time we need to post a new version of Bob that does not bring incompatible API modifications, that number is increased. For example, version 1.0.0 is the first release of Bob. Version 1.0.1 would be the first patch release.

Note

The numbering scheme for your package and Bob‘s may look the same, but should be totally independent of each other. Bob may be on version 3.4.2 while your package, still compatible with that release could be on 1.4.5. You should state on your setup.py file which version of Bob your package is compatible with, using the standard notation defined for setuptools installation requirements for packages.

You may use version number extenders for alpha, beta, and candidate releases with the above scheme, by appending aN, bN or cN to the version number. The value of N should be an integer starting at zero. Python’s setuptools package will correctly classifier package versions following this simple scheme. For more information on package numbers, consult Python’s PEP 386. Here are lists of valid python version numbers following this scheme:

0.0.1
0.1.0a35
1.2.3b44
2.4.99c32

Release Methodology for Satellite Packages

Here is a set of steps we recommend you follow when releasing a new version of your satellite package:

1. First decide on the new version number your package will get. If you are making a minor, API preserving, modification on an existing stable package (already published on PyPI), just increment the last digit on the version. Bigger changes may require that you signal them to users by changing the first digits of the package. Alpha, beta or candidate releases don’t need to have their main components of the version changed, just bump-up the last digit. For example 1.0.3a3 would become 1.0.3a4;

2. In case you are making an API modification to your package, you should think if you would like to branch your repository at this position. You don’t have to care about this detail with new packages, naturally.

   If required, branching will allow you to still make modifications (patches) on the old version of the code and develop on the master branch for the new release, in parallel. It is important to branch when you break functionality on existing code - for example to reach compatibility with an upcoming version of Bob. After a few major releases, your repository should look somewhat like this:

   ----> time
   
   initial commit
   o---------------o---------o-----o-----------------------> master
                   |         |     |
                   |         |     |   v2.0.0
                   |         |     +---x----------> 2.0
                   |         |
                   |         | v1.1.0  v1.1.1
                   |         +-x-------x------> 1.1
                   |
                   |   v1.0.0  v1.0.1a0
                   +---x-------x-------> 1.0

   The o‘s mark the points in which you decided to branch your project. The x‘s mark places where you decided to release a new version of your satellite package on PyPI. The -‘s mark commits on your repository. Time flies from left to right.

   In this ficticious representation, the master branch continue under development, but one can see older branches don’t receive much attention anymore.

   Here is an example for creating a branch at github (many of our satellite packages are hosted there). Let’s create a branch called 1.1:

   $ git branch 1.1
   $ git checkout 1.1
   $ git push origin 1.1

3. When you decide to release something publicly, we recommend you tag the version of the package on your repository, so you have a marker to what code you actually published on PyPI. Tagging on github would go like this:

   $ git tag v1.1.0
   $ git push && git push --tags

   Notice use prefix tag names with v.

4. Finally, after branching and tagging, it is time for you to publish your new package on PyPI. When the package is ready and you have tested it, just do the following:

   $ python setup.py register #if you modified your setup.py or README.rst
   $ python setup.py sdist --formats=zip upload

5. Announce the update on the relevant channels.

Satellite Packages Available

Look here for our growing list of Satellite Packages.