IPython Notebook - early exit from cell

To stop current and subsequent cells quietly:

class StopExecution(Exception):
    def _render_traceback_(self):
        pass

raise StopExecution

Slightly more "proper" options:

This will get you out of all but the worst try/except blocks.

raise KeyboardInterrupt

A little cleaner version of yours:

assert(False)

or simply:

raise

if you want to save a couple keystrokes.