Reported in https://github.com/mongodb/mongo-python-driver/pull/419. A user is periodically seeing InvalidBSON errors that have an empty error message, eg InvalidBSON(''). In that thread, the root cause was determined to be a MemoryError with an empty error message.

PyMongo could give the user more information in this case by including the original error's class name, eg: InvalidBSON('MemoryError: ').

Another option would be to always include the original class name.