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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 _before_insert(mapper, connection, target):
 """Set item to last position if position not defined."""

    if target.position is None:
        func = sa.sql.func
        stmt = sa.select([func.coalesce(func.max(mapper.mapped_table.c.position), -1)])
        target.position = connection.execute(stmt).scalar() + 1