Fixed #16245 -- Included traceback in send_robust()'s response

        If any receiver raises an error (specifically any subclass of

        Exception), the error instance is returned as the result for that

        receiver.

        receiver. The traceback is always attached to the error at

        ``__traceback__``.

        """

        responses = []

        if not self.receivers or self.sender_receivers_cache.get(sender) is NO_RECEIVERS:

            try:

                response = receiver(signal=self, sender=sender, **named)

            except Exception as err:

                if not hasattr(err, '__traceback__'):

                    err.__traceback__ = sys.exc_info()[2]

                responses.append((receiver, err))

            else:

                responses.append((receiver, response))

Signals

^^^^^^^

* ...

* Exceptions from the ``(receiver, exception)`` tuples returned by

  :meth:`Signal.send_robust() <django.dispatch.Signal.send_robust>` now have

  their traceback attached as a ``__traceback__`` attribute.

Templates

^^^^^^^^^

and ensures all receivers are notified of the signal. If an error occurs, the

error instance is returned in the tuple pair for the receiver that raised the error.

.. versionadded:: 1.8

    The tracebacks are present on the ``__traceback__`` attribute

    of the errors returned when calling ``send_robust()``.

Disconnecting signals

=====================

import time

import unittest

import weakref

from types import TracebackType

from django.dispatch import Signal, receiver

        err = result[0][1]

        self.assertIsInstance(err, ValueError)

        self.assertEqual(err.args, ('this',))

        self.assertTrue(hasattr(err, '__traceback__'))

        self.assertTrue(isinstance(err.__traceback__, TracebackType))

        a_signal.disconnect(fails)

        self._testIsClean(a_signal)