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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 build_if_needed(db):
 """Little helper method for making tables in SQL-Alchemy with SQLite"""

    if len(db.engine.table_names()) == 0:
        # import all classes here
        from my_site.models.tables.user import User

        db.create_all()