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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def _add_to(self, db, index, item, default=OOSet):
 """ Add `item` to `db` under `index`. If `index` is not yet in `db`, create it using `default`. Args: db (dict-obj):
 Dict-like object used to connect to database. index (str):
 Index used to look in `db`. item (obj):
 Persistent object, which may be stored in DB. default (func/obj):
 Reference to function/object, which will be used to create the object under `index`. Default :class:`OOSet`. """

        row = db.get(index, None)

        if row is None:
            row = default()
            db[index] = row

        row.add(item)