sqlalchemy里engine.execute('select 1').scalar()是什么意思？

Question

sqlalchemy里engine.execute('select 1').scalar()是什么意思？
select 1 是什么？
scalar()这个方法是什么意思，怎么用呀？

In [25]: import sqlalchemy

In [26]: engine = create_engine('mysql+mysqldb://root:aptech@localhost:3306/test',echo=True)

In [27]: engine.execute('select 1').scalar()
2015-04-16 17:24:22,277 INFO sqlalchemy.engine.base.Engine SHOW VARIABLES LIKE 'sql_mode'
2015-04-16 17:24:22,277 INFO sqlalchemy.engine.base.Engine ()
2015-04-16 17:24:22,278 INFO sqlalchemy.engine.base.Engine SELECT DATABASE()
2015-04-16 17:24:22,278 INFO sqlalchemy.engine.base.Engine ()
2015-04-16 17:24:22,279 INFO sqlalchemy.engine.base.Engine show collation where Charset = 'utf8' and Collation = 'utf8_bin'
2015-04-16 17:24:22,279 INFO sqlalchemy.engine.base.Engine ()
2015-04-16 17:24:22,281 INFO sqlalchemy.engine.base.Engine SELECT CAST('test plain returns' AS CHAR(60)) AS anon_1
2015-04-16 17:24:22,281 INFO sqlalchemy.engine.base.Engine ()
2015-04-16 17:24:22,282 INFO sqlalchemy.engine.base.Engine SELECT CAST('test unicode returns' AS CHAR(60)) AS anon_1
2015-04-16 17:24:22,282 INFO sqlalchemy.engine.base.Engine ()
2015-04-16 17:24:22,283 INFO sqlalchemy.engine.base.Engine SELECT CAST('test collated returns' AS CHAR CHARACTER SET utf8) COLLATE utf8_bin AS anon_1
2015-04-16 17:24:22,284 INFO sqlalchemy.engine.base.Engine ()
2015-04-16 17:24:22,285 INFO sqlalchemy.engine.base.Engine select 1
2015-04-16 17:24:22,285 INFO sqlalchemy.engine.base.Engine ()
Out[27]: 1L