When trying to use $inc I get a Syntax error stating that $set is wrong. My query is as follow:
mongo_db.campaign.update({\'_id\': str(campaign_id)}, { $inc:
$inc
isn't a valid Python identifier. You should pass it as a string, like everything else:
mongo_db.campaign.update({'_id': str(campaign_id)}, {'$inc': {'item': 1}})
The MongoDB docs you linked are the general MongoDB documentation, not PyMongo-specific; you can't copy/paste them literally and expect things to work.