ipython/traitlets — pull request #2 by satra (2014-01-02 20:18:48+00:00)
Title: WIP: refactoring traitlets to support nipype requirements

The main additions are:

- Dict
- Either
- File
- Directory

This PR primarily serves as a placeholder for changes required to support nipype. It may turn out that some of these changes are orthogonal to IPython's view of traitlets (for example, support for Undefined as a valid value for any trait).