Add __repr__ for NovaException

Due to change c1a7079c26d27a2e46cca26963d3d9aa040bdbe8 in
oslo.serialization, serialized exceptions in errors no longer
have kwargs. This change fixes the problem by adding __repr__
to NovaException which will return a string representation
of exception.__dict__. This string contains the exception message
along with all the kwargs. Without __repr__, the serialization
process for exceptions just returns the exception type and the
default message, without the kwargs.

Change-Id: I653282a030d03362dfca0fd1026cebe920d54e37
Closes-Bug: #1756360

nova/exception.py

@@ -102,6 +102,11 @@ class NovaException(Exception):
         # which should be our full NovaException message, (see __init__)
         return self.args[0]
 
+    def __repr__(self):
+        dict_repr = self.__dict__
+        dict_repr['class'] = self.__class__.__name__
+        return str(dict_repr)
+
 
 class EncryptionFailure(NovaException):
     msg_fmt = _("Failed to encrypt text: %(reason)s")

nova/tests/unit/test_exception.py

@@ -229,6 +229,23 @@ class NovaExceptionTestCase(test.NoDBTestCase):
         exc = FakeNovaException_Remote(lame_arg='lame')
         self.assertEqual("some message %(somearg)s", exc.format_message())
 
+    def test_repr(self):
+        class FakeNovaException(exception.NovaException):
+            msg_fmt = "some message"
+
+        mock_exc = FakeNovaException(code=500)
+
+        exc_repr = repr(mock_exc)
+
+        eval_repr = eval(exc_repr)
+        exc_kwargs = eval_repr.get('kwargs')
+
+        self.assertIsNotNone(exc_kwargs)
+
+        self.assertEqual(500, exc_kwargs.get('code'))
+        self.assertEqual('some message', eval_repr.get('message'))
+        self.assertEqual('FakeNovaException', eval_repr.get('class'))
+
 
 class ConvertedExceptionTestCase(test.NoDBTestCase):
     def test_instantiate(self):