The unittest.TestCase.assertEqual() now displays the differences in lists,

The unittest.TestCase.assertEqual() now displays the differences in lists,
tuples, dicts and sets on failure.

Many new handy type and comparison specific assert* methods have been added
that fail with error messages actually useful for debugging.  Contributed in
by Google and completed with help from mfoord and GvR at PyCon 2009 sprints.

Discussion lives in http://bugs.python.org/issue2578.