Under python 2 when an atexit callback raised an exception the full traceback was displayed. Under python 3, only the summary of the exception is shown.

Input file:

import atexit


def exit_with_exception(message):
    raise RuntimeError(message)

atexit.register(exit_with_exception, 'Registered first')
atexit.register(exit_with_exception, 'Registered second')


Python 2:

$ python2.7 source/atexit/atexit_exception.py
Error in atexit._run_exitfuncs:
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/atexit.py", line 24, in _run_exitfuncs
    func(*targs, **kargs)
  File "source/atexit/atexit_exception.py", line 36, in exit_with_exception
    raise RuntimeError(message)
RuntimeError: Registered second
Error in atexit._run_exitfuncs:
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/atexit.py", line 24, in _run_exitfuncs
    func(*targs, **kargs)
  File "source/atexit/atexit_exception.py", line 36, in exit_with_exception
    raise RuntimeError(message)
RuntimeError: Registered first
Error in sys.exitfunc:
Traceback (most recent call last):
  File "/Library/Frameworks/Python.framework/Versions/2.7/lib/python2.7/atexit.py", line 24, in _run_exitfuncs
    func(*targs, **kargs)
  File "source/atexit/atexit_exception.py", line 36, in exit_with_exception
    raise RuntimeError(message)
RuntimeError: Registered first

Python 3:

$ python3.3 source/atexit/atexit_exception.py
Error in atexit._run_exitfuncs:
RuntimeError: Registered second
Error in atexit._run_exitfuncs:
RuntimeError: Registered first

The attached patch fixes two instances of PyErr_Display being called without the traceback properly set on the exception object.

Attached patch does the setting in PyErr_Display (which is an undocumented API, thus presumably private), and adds a test for atexit.

With your patch, can the SetTraceback in PyErr_Print be removed?
Or should PyErr_Display only set the tb if there is none on the object already?

> With your patch, can the SetTraceback in PyErr_Print be removed?

I don't think so. PyErr_Print() calls sys.excepthook, which can be
overriden with custom code.

> Or should PyErr_Display only set the tb if there is none on the
> object already?

Well, why not!

Updated patch.

New changeset 19ce90930e8b by Antoine Pitrou in branch '3.3':
Issue #18776: atexit callbacks now display their full traceback when they raise an exception.
http://hg.python.org/cpython/rev/19ce90930e8b

New changeset c13ef65f3dcf by Antoine Pitrou in branch 'default':
Issue #18776: atexit callbacks now display their full traceback when they raise an exception.
http://hg.python.org/cpython/rev/c13ef65f3dcf

Since it's a regression from 2.7, I chose to commit it as a bugfix (to 3.3 and 3.4).