Avoid exc_info cycles in several places and comment on trickier ones

testtools/run.py

@@ -187,9 +187,7 @@ class TestProgram(object):
                 self.testNames = (self.defaultTest,)
             self.createTests()
         except getopt.error:
-            exc_info = sys.exc_info()
-            msg = exc_info[1]
-            self.usageExit(msg)
+            self.usageExit(sys.exc_info()[1])
 
     def createTests(self):
         if self.testNames is None:

testtools/runtest.py

@@ -146,8 +146,11 @@ class RunTest(object):
             raise
         except:
             exc_info = sys.exc_info()
-            e = exc_info[1]
-            self.case.onException(exc_info)
+            try:
+                e = exc_info[1]
+                self.case.onException(exc_info)
+            finally:
+                del exc_info
             for exc_class, handler in self.handlers:
                 if isinstance(e, exc_class):
                     self._exceptions.append(e)

testtools/testcase.py

@@ -179,8 +179,11 @@ class TestCase(unittest.TestCase):
                 raise
             except:
                 exc_info = sys.exc_info()
-                self._report_traceback(exc_info)
-                last_exception = exc_info[1]
+                try:
+                    self._report_traceback(exc_info)
+                    last_exception = exc_info[1]
+                finally:
+                    del exc_info
         return last_exception
 
     def addCleanup(self, function, *arguments, **keywordArguments):
@@ -319,9 +322,14 @@ class TestCase(unittest.TestCase):
         try:
             predicate(*args, **kwargs)
         except self.failureException:
+            # GZ 2010-08-12: Don't know how to avoid exc_info cycle as the new
+            #                unittest _ExpectedFailure wants old traceback
             exc_info = sys.exc_info()
-            self._report_traceback(exc_info)
-            raise _ExpectedFailure(exc_info)
+            try:
+                self._report_traceback(exc_info)
+                raise _ExpectedFailure(exc_info)
+            finally:
+                del exc_info
         else:
             raise _UnexpectedSuccess(reason)
 

testtools/tests/helpers.py

@@ -12,6 +12,7 @@ __all__ = [
 from testtools import TestResult
 
 
+# GZ 2010-08-12: Don't do this, pointlessly creates an exc_info cycle
 try:
     raise Exception
 except Exception: