Debug on exceptions decorator.

debug_on.py

# http://stackoverflow.com/a/4399246/143097

import unittest
import sys
import pdb
import functools
import traceback

def debug_on(*exceptions):
    if not exceptions:
        exceptions = (AssertionError, )
    def decorator(f):
        @functools.wraps(f)
        def wrapper(*args, **kwargs):
            try:
                return f(*args, **kwargs)
            except exceptions:
                info = sys.exc_info()
                traceback.print_exception(*info)
                pdb.post_mortem(info[2])
        return wrapper
    return decorator
  
class tests(unittest.TestCase):
    @debug_on()
    def test_trigger_pdb(self):
        assert False

For nosetests just:

nosetests --pdb