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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 _apply_sort(cursor, sort_by, sort_direction):
 """ Apply sort to a cursor. :param cursor: The cursor to apply sort on. :param sort_by: The field name to sort by. :param sort_direction: The direction to sort, "asc" or "desc". :return: """

        if sort_direction is not None and sort_direction.lower() == "desc":
            sort = pymongo.DESCENDING
        else:
            sort = pymongo.ASCENDING
        return cursor.sort(sort_by, sort)