### limit、offset和切片操作：
1. limit：可以限制每次查询的时候只查询几条数据。2. offset：可以限制查找数据的时候过滤掉前面多少条。3. 切片：可以对Query对象使用切片操作，来获取想要的数据。可以使用`slice(start,stop)`方法来做切片操作。也可以使用`[start:stop]`的方式来进行切片操作。一般在实际开发中，中括号的形式是用得比较多的。示例代码如下：1 # coding:utf-8 2 3 from datetime import datetime 4 from sqlalchemy import create_engine, Column, Integer, String, DateTime 5 6 from sqlalchemy.ext.declarative import declarative_base 7 from sqlalchemy.orm import sessionmaker, relationship, backref 8 9 HOSTNAME = '127.0.0.1'10 PORT = 330611 DATABASE = 'sqlalchemy_first'12 USERNAME = 'root'13 PASSWORD = '123456'14 15 DB_URI = 'mysql+pymysql://{username}:{password}@{host}:{port}/{dbname}?charset=utf8'.format(16 username=USERNAME, password=PASSWORD, host=HOSTNAME, port=PORT, dbname=DATABASE17 )18 engine = create_engine(DB_URI)19 Base = declarative_base(engine)20 Session = sessionmaker(engine)21 session = Session()22 23 24 class Article(Base):25 __tablename__ = 'article'26 id = Column(Integer, primary_key=True, autoincrement=True)27 title = Column(String(50), nullable=False)28 createtime = Column(DateTime, nullable=False, default=datetime.now)29 30 def __repr__(self):31 return "Article ".format(self.title)32 33 34 Base.metadata.drop_all()35 Base.metadata.create_all()36 37 for _ in xrange(100):38 article = Article(title='article{}'.format(_))39 session.add(article)40 session.commit()41 42 43 # limit44 articles = session.query(Article).limit(10).all()45 print articles46 47 # offset48 articles = session.query(Article).offset(10).limit(10).all()49 print articles50 51 # slice, sliece(start, end) 从start取到end.52 articles = session.query(Article).slice(10, 20).all()53 print articles54 55 56 # 切片57 articles = session.query(Article)[0:10]58 print articles