Fixed #20028 -- Made atomic usable on callable instances.

from functools import wraps

from django.db import connections, DatabaseError, DEFAULT_DB_ALIAS

from django.utils.decorators import available_attrs

class TransactionManagementError(Exception):

    def __call__(self, func):

        @wraps(func)

        @wraps(func, assigned=available_attrs(func))

        def inner(*args, **kwargs):

            with self:

                return func(*args, **kwargs)

                transaction.leave_transaction_management()

class AtomicMiscTests(TransactionTestCase):

    def test_wrap_callable_instance(self):

        # Regression test for #20028

        class Callable(object):

            def __call__(self):

                pass

        # Must not raise an exception

        transaction.atomic(Callable())

class IgnorePendingDeprecationWarningsMixin(object):

    def setUp(self):