Unable to deserialize PyMongo ObjectId from JSON

I think your string form actually looks like the python representation...

s = '{"_id": {"$oid": "4edebd262ae5e93b41000000"}}'u = json.loads(s, object_hook=json_util.object_hook)print u  # Result:  {u'_id': ObjectId('4edebd262ae5e93b41000000')}s = json.dumps(u, default=json_util.default)print s  # Result:  {"_id": {"$oid": "4edebd262ae5e93b41000000"}}

The bson.json_util.object_hook function does not seem to have any type of handling for there being ObjectId() in the actual json string representation.

There are two problems here:

1. The string you're attempting to JSON-decode is not JSON, it's the string representation of a Python dictionary. In particular, the problem is that u'_id' is not a valid JSON key (JSON keys are quoted strings; the "u" here indicates a Python unicode string, which is meaningless in JSON)

2. json_util.object_hook doesn't make ObjectId available to JSON; the json module will decode the JSON, and then call the object_hook callback with each decoded object. json_util.object_hook will look for certain patterns as defined in the strict mode of MongoDB Extended JSON.

See @jdi's answer for examples of how to properly use json_util.