How do I do a get_or_create in pymongo (python mongodb)?

You can use "upsert" equal to true. Then the update query you run with "upsert" as true will do exactly what you want.

• update if exists.
• insert new if it does not exist.

From MongoDb documentation:

db.collection.update( criteria, objNew, upsert, multi )

Arguments:

    criteria - query which selects the record to update;
    objNew - updated object or $ operators (e.g., $inc) which manipulate the object
    upsert - if this should be an "upsert"; that is, if the record does not exist, insert it
    multi - if all documents matching criteria should be updated

http://www.mongodb.org/display/DOCS/Updating

Example:

db.test.update({"x": "42"}, {"$set": {"a": "21"}},True)    
#True => Upsert is True

See "update" documentation here :

http://api.mongodb.org/python/current/api/pymongo/collection.html

http://api.mongodb.org/python/current/api/pymongo/collection.html#pymongo.collection.Collection.update

Set upsert=True