[Twisted-Python] Trial __del__ behavior change - intentional?

[Scott Lamb]

I'm seeing a weird thing on Twisted 2.2.0. It does not happen with  
older versions of Twisted (trunk revision 16674, which I had sitting  
around for some reason). It appears I can't use reference handling to  
clean up resources within a trial - the output code apparently keeps  
a reference to the stack trace or something until after it's done.  
That's too late for me - this resource is essentially a mutex, so if  
I have more than one TestCase in a single trial run, my tests don't  
work.

Is this change intentional?

My test code's inline, along with results on both versions. I'm not  
quite sure how make proper unit tests of trial itself, so  
unfortunately you must interpret the results manually.

$ cat resource_test.py
#!/usr/bin/env
"""A test of using __del__ for cleaning up resources within trial tests.

On trunk revision 16674, this works fine. On Twisted 2.2.0, something  
holds
an extra reference to my resource object. Python actually exits without
ever calling my __del__.
"""

from twisted.trial import unittest

class MyResource:
     def __init__(self, cleaned_up):
         print '<<<INIT CALLED>>>'
         self.cleaned_up = cleaned_up

     def __del__(self):
         print '<<<DEL CALLED>>>'
         self.cleaned_up[0] = True

     def raiseerror(self):
         raise Exception('foo')

class ReferenceTest(unittest.TestCase):
     def setUp(self):
         # This is an array so that the callee can make changes that  
alter
         # our copy.
         self.cleaned_up = [False]
         self.my_resource = MyResource(self.cleaned_up)

     def tearDown(self):
         self.my_resource = None
         self.assertEquals(self.cleaned_up[0], True)

     def testError(self):
         self.my_resource.raiseerror()

     def testPass(self):
         pass


[machine-a ~]$ svnversion svn/Twisted
16674
[machine-a ~]$ trial resource_test
   resource_test
     ReferenceTest
<<<INIT CALLED>>>
       testError ... <<<DEL CALLED>>>
                                                     [ERROR]
<<<INIT CALLED>>>
       testPass ... <<<DEL CALLED>>>
                                                         [OK]

======================================================================== 
=======
[ERROR]: resource_test.ReferenceTest.testError

   File "twisted/internet/defer.py", line 109, in maybeDeferred

   File "/Users/slamb/resource_test.py", line 35, in testError
     self.my_resource.raiseerror()
   File "/Users/slamb/resource_test.py", line 21, in raiseerror
     raise Exception('foo')
exceptions.Exception: foo
------------------------------------------------------------------------ 
-------
Ran 2 tests in 0.030s

FAILED (errors=1, successes=1)

[machine-b ~]$ rpm -q python-twisted
python-twisted-2.2.0-1
[machine-b ~]$ trial resource_test
Running 2 tests.
resource_test
   ReferenceTest
     testError ... <<<INIT CALLED>>>
                                                       [ERROR]
                                                       [ERROR]
   tearDown                                                          
['ERROR']
     testPass ... <<<INIT CALLED>>>
<<<DEL CALLED>>>
                                                           [OK]

======================================================================== 
=======
[ERROR]: resource_test.ReferenceTest.testError

   File "/home/slamb/resource_test.py", line 35, in testError
     self.my_resource.raiseerror()
   File "/home/slamb/resource_test.py", line 21, in raiseerror
     raise Exception('foo')
exceptions.Exception: foo
======================================================================== 
=======
[ERROR]: resource_test.ReferenceTest.testError

   File "/home/slamb/resource_test.py", line 32, in tearDown
     self.assertEquals(self.cleaned_up[0], True)
twisted.trial.unittest.FailTest: False != True
------------------------------------------------------------------------ 
-------
Ran 2 tests in 0.055s

FAILED (errors=2, successes=1)
<<<DEL CALLED>>>

-- 
Scott Lamb <http://www.slamb.org/>