The pymongo documentation you pointed is obsolete. If you’re using version 1.7 I recommend updating. With a more recent version you can do this:
from bson.json_util import dumps
dumps(l)
https://pymongo.readthedocs.io/en/stable/api/bson/json_util.html
Side answer: u'name', u'date', u'_id' etc are the names of the fields of the document on the database.