Is it possible to have a bulk operation in MongoDB (with python) where insert and update commands are mixed? Updated records can be the ones that would be inserted in the same batch.
Yes. PyMongo 2.7 added a "Bulk API" which you can read about here. PyMongo 3.0 is adding an alternative API to do the same thing that is very similar to what you mention in a comment to another answer. See this commit for a preview.