astropy/astropy — pull request #353 by astrofrog (2012-08-19 15:44:34+00:00)
Title: Disable compatibility packages by default, and require 'all or nothing'

As discussed off list with the maintainers of the packages using compatibility packages, it may be preferable to not have the compatibility packages enabled by default. Here's a summary of the reasons:

* they install something the user didn't ask for explicitly
* they cause issues with package managers, especially regarding conflicts with the original packages
* they discourage users from migrating to Astropy
* they can cause issues with existing scripts and programs

The issue is also that users don't realize the implications of having the compatibility layers, so by disabling them by default, the users have to read the docs to understand what this does, and that is is experimental.

In addition, since users can have issues if e.g. `pyfits` is the original package and `pywcs` is the compatibility package, the compatibility packages are only installed if *none* of the original packages are present. There might be a better way of doing this last point - suggestions welcome.