MAINT: Make exception handling tests compatible between Python 2 and 3

Python 3 removes the `.message` attribute, so use `str` instead.

Also, the divide by zero message has changed slightly between versions,
so just check for the exception type, instead of also checking the message.

tests/test_exception_handling.py

@@ -57,14 +57,9 @@ class ExceptionTestCase(TestCase):
             **self.zipline_test_config
         )
 
-        with self.assertRaises(ZeroDivisionError) as ctx:
+        with self.assertRaises(ZeroDivisionError):
             output, _ = drain_zipline(self, zipline)
 
-        self.assertEqual(
-            ctx.exception.message,
-            'integer division or modulo by zero'
-        )
-
     def test_tranform_exception(self):
         exc_tnfm = StatefulTransform(ExceptionTransform)
         self.zipline_test_config['transforms'] = [exc_tnfm]
@@ -76,7 +71,7 @@ class ExceptionTestCase(TestCase):
         with self.assertRaises(AssertionError) as ctx:
             output, _ = drain_zipline(self, zipline)
 
-        self.assertEqual(ctx.exception.message,
+        self.assertEqual(str(ctx.exception),
                          'An assertion message')
 
     def test_exception_in_handle_data(self):
@@ -96,7 +91,7 @@ class ExceptionTestCase(TestCase):
         with self.assertRaises(Exception) as ctx:
             output, _ = drain_zipline(self, zipline)
 
-        self.assertEqual(ctx.exception.message,
+        self.assertEqual(str(ctx.exception),
                          'Algo exception in handle_data')
 
     def test_zerodivision_exception_in_handle_data(self):
@@ -113,12 +108,9 @@ class ExceptionTestCase(TestCase):
             **self.zipline_test_config
         )
 
-        with self.assertRaises(ZeroDivisionError) as ctx:
+        with self.assertRaises(ZeroDivisionError):
             output, _ = drain_zipline(self, zipline)
 
-        self.assertEqual(ctx.exception.message,
-                         'integer division or modulo by zero')
-
     def test_set_portfolio(self):
         """
         Are we protected against overwriting an algo's portfolio?
@@ -136,8 +128,5 @@ class ExceptionTestCase(TestCase):
             **self.zipline_test_config
         )
 
-        with self.assertRaises(AttributeError) as ctx:
+        with self.assertRaises(AttributeError):
             output, _ = drain_zipline(self, zipline)
-
-        self.assertEqual(ctx.exception.message,
-                         "can't set attribute")

zipline/utils/test_utils.py

@@ -95,6 +95,9 @@ class ExceptionSource(object):
     def next(self):
         5 / 0
 
+    def __next__(self):
+        5 / 0
+
 
 class ExceptionTransform(object):