Make vertica_python.errors classes (un)picklable (#374)

Author: DerrickRice

vertica_python/errors.py

@@ -137,6 +137,17 @@ def one_line_sql(self):
         else:
             return ''
 
+    def __reduce__(self):
+        # Workaround to make these exception instances (un)picklable. This must
+        # be redefined by any subclass that changes the signature of __init__
+        #
+        # This workaround applies to python3. https://bugs.python.org/issue37489
+        return (
+            type(self),
+            (self.error_response, self.sql),
+            self.__dict__,
+        )
+
     @property
     def _notice_attrs(self):
         # provided for _NoticeResponseAttrMixin

vertica_python/tests/unit_tests/test_errors.py

@@ -0,0 +1,50 @@
+# Copyright (c) 2018-2020 Micro Focus or one of its affiliates.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#    http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+
+
+from __future__ import print_function, division, absolute_import
+
+from .base import VerticaPythonUnitTestCase
+from ...errors import VerticaSyntaxError
+from ...vertica.messages.backend_messages.error_response import ErrorResponse
+
+import pickle
+
+# Using a subclass of ErrorResponse for this test, to avoid the complexity of
+# creating an ErrorResponse object. At the time of writing, ErrorResponse and
+# other BackendMessage instances can only be created from server-provided data.
+#
+# This subclass allows for simpler instantiation without binding to any details
+# of server data serialization, a la NoticeResponseAttrMixin and NoticeResponse
+class MockErrorResponse(ErrorResponse):
+    def __init__(self):
+        # does NOT call super
+        self._notice_attrs = {}
+
+    def error_message(self):
+        return "Manufactured error message for testing"
+
+class ErrorsTestCase(VerticaPythonUnitTestCase):
+    def test_pickling(self):
+        err_response = MockErrorResponse()
+        sql = "select 1;"
+        exc = VerticaSyntaxError(err_response, sql)
+
+        serde = pickle.loads(pickle.dumps(exc))
+
+        assert isinstance(serde, VerticaSyntaxError)
+        assert str(serde) == str(exc)
+        assert isinstance(serde.error_response, MockErrorResponse)
+        assert serde.error_response.error_message() == err_response.error_message()
+        assert serde.sql == exc.sql