When an exception is raised in a __del__ method or a finalizer (i.e. a
weakref callback), only the exception name is printed out.

Unfortunately, arbitrarily complex code can be involved which makes
debugging quite tedious. It would be nice to display the full traceback,
so that these errors are easier to diagnose.

The same bug was reported in the past, but it was fixed for Python 3.3 onwards.

Since it is trivial to get this fix in Python 2.7, I'm adding the patch for it here.