This sub-package contains third-party Python packages/modules that are required for some of Astropy's core functionality. It also contains third- party JavaScript libraries used for browser-based features.

In particular, this currently includes for Python:

• ConfigObj (Python 2 and 3 versions): This provides the core config file handling for Astropy's configuration system.
• PLY: This is a parser generator providing lex/yacc-like tools in Python. It is used for Astropy's unit parsing and angle/coordinate string parsing.
• pytest: This is the test framework used to collect and run Astropy's tests. It is a fairly large package, so it is bundled as a compressed base64 string that is unpacked and loaded as a Python module. This packed bundled version is officially provided by the pytest project.
• Six: This is a Python 2/3 compatibility library used to ease development of a simultaneously Python 2 and 3-compatible code base.

And for JavaScript:

• jQuery: This is used currently for the browser-based table viewer feature.
• DataTables: This is a plug-in for jQuery used also for the browser-based table viewer.

the minified files are the ones that are used in the table viewer feature, but the non-minified versions are also present in the js/ sub-directory for packaging reasons. These files must also be distributed, to provide the source files from which the minified ones can be compiled. This is a requirement for Linux distributions such as Debian and Fedora.

Packagers preparing Astropy for inclusion in packaging frameworks have different options for how to handle these third-party extern packages, if they would prefer to use their system packages rather than the bundled versions.

Because use of the six module is pervasive throughout the Astropy package (it is crucial for providing Python 2/3 compatibility at all levels) it has been made easier to replace. The actual six module is included under astropy/extern/bundled. Importing astropy.extern.six will first try to load the six module from that location, and then will fall back on trying to import an installed six module from the standard sys.path locations (if it is a new enough version).

Packagers may wish to prioritize the system version and/or remove the bundled version altogether. To do this, edit the _SIX_SEARCH_PATH list in astropy.extern.six. If removing the bundled copy altogether simply delete astropy/extern/bundled/six.py and update this variable to read:

_SIX_SEARCH_PATH = ['six']

No other imports in Astropy need to be updated. Imports from astropy.extern.six are automatically updated to point to the system version of the module.

Packagers may either use system copies of these JavaScript modules, or require use of online versions (perhaps via URLs of cloud-hosted versions of these modules).

It is possible to change the default urls for the remote versions of these files by using the Astropy Configuration system. The default configuration file ($HOME/.astropy/config) contains a commented section [table.jsviewer] with two items for jQuery and DataTables. It is also possible to display the default value and modify it by importing the configuration module:

In [1]: from astropy.table.jsviewer import conf

In [2]: conf.jquery_url
Out[2]: u'https://code.jquery.com/jquery-1.11.3.min.js'

In [3]: conf.jquery_url = '...'

Third-party packagers can override the defaults for these configuration items (by modifying the configuration objects in astropy/table/jsviewer.py, or provide astropy config files that include the overrides appropriate for the packaged version. They would also need to set the default use_local_files option to False for these settings to be read.

To replace any of the other Python modules included in this package, simply remove them and update any imports in Astropy to import the system versions rather than the bundled copies. If requested we could add a mechanism similar to that used by six for the other modules.