def __missing__(self, key):
self[key] = self.default_factory(self, key)<EOL>return self[key]<EOL>
Automatically called when the given date (key) doesn't exist. In that
case, create the EntriesList for that key, attach it the entries
collection (to allow callbacks when an item is added/removed) and the
date. Also if we're in synchronized mode, add the date line to the
textual representation.