Date/time format when parsing document from mongo extended json

[landler]

Currently there doesn't seem to be a way to properly parse mongodb extended json datetimes into a document with from_json. As an example consider this extended json document:

{
   "id" : {"$oid": "507f1f77bcf86cd799439011"},
   "time" : {"$date" : 18000000}
}

The id is properly parsed with a structure as follows:

{
    "id" : bson.objectid.ObjectId,
    "time": datetime.datetime
}

However, parsing the date fails since mongokit/document.py:586 just calls fromtimestamp with the whole {"$date".. dict as an argument. This could be solved by using a structure where "time": {"$date": datetime.datetime}, but this doesn't work since keys starting with $ are not allowed.

It seems to me it would be optimal if mongokit would be able to parse the standard mongodb extended json out of the box - for a variety of reasons. Thus it would probably make sense to either replace line 586 with doc[key] = fromtimestamp(doc[key]["$date"]) , (just like is done with $oid for objectid fields or $db and $ref) or if there are fears of breaking backwards compatibility by checking the type of doc[key] and whether there is a $date key if it is a dict. I can fork and make a pull request if you agree with my reasoning.

On a related note, since mongodb 2.6 the extended json format also uses ISO datetime strings instead of milliseconds since epoch - so the current parser fails there as well.