PYTHON-1966 Fix unicode(PyMongoError) on Python 2

Author: ShaneHarvey

pymongo/errors.py

@@ -46,10 +46,16 @@ def _remove_error_label(self, label):
         """Remove the given label from this error."""
         self._error_labels.remove(label)
 
-    def __str__(self):
-        if sys.version_info[0] == 2 and isinstance(self._message, unicode):
-            return self._message.encode('utf-8', errors='replace')
-        return str(self._message)
+    if sys.version_info[0] == 2:
+        def __str__(self):
+            if isinstance(self._message, unicode):
+                return self._message.encode('utf-8', errors='replace')
+            return str(self._message)
+
+        def __unicode__(self):
+            if isinstance(self._message, unicode):
+                return self._message
+            return unicode(self._message, 'utf-8', errors='replace')
 
 
 class ProtocolError(PyMongoError):

test/test_collection.py

@@ -1335,6 +1335,12 @@ def test_write_error_unicode(self):
         self.assertIn('E11000 duplicate key error',
                       str(ctx.exception))
 
+        if sys.version_info[0] == 2:
+            # Test unicode(error) conversion.
+            self.assertIn('E11000 duplicate key error',
+                          unicode(ctx.exception))
+
+
     def test_wtimeout(self):
         # Ensure setting wtimeout doesn't disable write concern altogether.
         # See SERVER-12596.