ipython/ipython — pull request #5033 by ellisonbg (2014-02-05 17:35:27+00:00)
Title: Add `HasTraits.on_change` as a simplified API for handler registration

This closes #5030

There are two things that this does:

* Adds `HasTraits.on_change(name, handler(value))`.
* Adds checks to make sure dynamic handlers are callable, when they are registered, rather than called.