add python_sqlalchemy, and fix bugs in python_base
xianhu
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431283a473
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4d0983d1f0
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@ -11,6 +11,8 @@
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### python_weibo.py: “史上最详细”的Python模拟登录新浪微博流程
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### python_lda.py: 玩点高级的--带你入门Topic模型LDA（小改进+附源码）
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### python_sqlalchemy: SQLAlchemy入门代码文档
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============================================================
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### 您可以fork该项目,并在修改后提交Pull request
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@ -137,8 +137,8 @@
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#-- 内置str处理函数：
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str1 = "stringobject"
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str1.upper(); str1.lower(); str1.swapcase(); str1.capitalize(); str1.title() # 全部大写，全部小写、大小写转换，首字母大写，每个单词的首字母都大写
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str1.ljust(width) # 获取固定长度，右对齐，左边不够用空格补齐
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str1.rjust(width) # 获取固定长度，左对齐，右边不够用空格补齐
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str1.ljust(width) # 获取固定长度，左对齐，右边不够用空格补齐
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str1.rjust(width) # 获取固定长度，右对齐，左边不够用空格补齐
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str1.center(width) # 获取固定长度，中间对齐，两边不够用空格补齐
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str1.zfill(width) # 获取固定长度，右对齐，左边不足用0补齐
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str1.find('t',start,end) # 查找字符串，可以指定起始及结束位置搜索
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@ -0,0 +1,95 @@
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# _*_ coding: utf-8 _*_
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"""
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python_sqlalchemy.py by xianhu
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"""
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import sqlalchemy
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import sqlalchemy.orm
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import sqlalchemy.ext.declarative
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# 利用数据库字符串构造engine, echo为True将打印所有的sql语句
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engine = sqlalchemy.create_engine("mysql+pymysql://username:password@hostname/dbname", encoding="utf8", echo=True)
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"""
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# 利用engine创建connection,这里不需要close操作
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with engine.connect() as conn:
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# 最基础的用法
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result = conn.execute("select * from tablename limit 10;")
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for item in result:
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print(item)
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# execute的几种用法,这里具体还是得参考pymysql的用法,这里不需要执行commit操作
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conn.execute("insert into tablename(id, url, title) values(1, "url1", "title1");")
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conn.execute("insert into tablename(id, url, title) values(%s, %s, %s);", 2, "url2", "title2")
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conn.execute("insert into tablename(id, url, title) values(%s, %s, %s)", (3, "url3", "title3"))
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conn.execute("insert into tablename(id, url, title) values(%s, %s, %s)", [(31, "url31", "title31"), (32, "url32", "title32")])
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# 使用事务可以进行批量提交和回滚
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trans = conn.begin()
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try:
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conn.execute("insert into tablename(id, url, title) values(%s, %s, %s)", [(4, "url4", "title4"), (5, "url5", "title5")])
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trans.commit()
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except Exception as excep:
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trans.rollback()
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raise
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"""
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# 利用ORM特性生成模型
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Base = sqlalchemy.ext.declarative.declarative_base()
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# 构建模型User
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class User(Base):
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__tablename__ = "User"
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id = sqlalchemy.Column("id", sqlalchemy.Integer, primary_key=True, autoincrement=True)
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name = sqlalchemy.Column("name", sqlalchemy.String(50), default="", unique=True)
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age = sqlalchemy.Column("age", sqlalchemy.Integer, nullable=False)
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# 利用Session对象连接数据库
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DBSessinon = sqlalchemy.orm.sessionmaker(bind=engine) # 创建会话类
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session = DBSessinon() # 创建会话对象
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# 创建表（如果表已经存在，则不会创建）
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Base.metadata.create_all(engine)
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try:
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# 清空数据,不需要commit操作
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session.query(User).filter(User.id != -1).delete()
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# 插入数据,这里的一个user只插入一次,第二次插入不生效
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user = User(name="tobi", age=20)
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session.add(user)
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session.commit()
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# 修改数据
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user.name = "allen"
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session.merge(user) # 使用merge方法,如果存在则修改,如果不存在则插入
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session.query(User).filter(User.id == user.id).update({"name": "carol"}) # 使用update方法
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# 查询数据
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users = session.query(User) # 返回全部结果
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for user in users:
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print(user.id, user.name, user.age)
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user = session.query(User).get(2) # 返回结果集的第二项
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users = session.query(User)[1:3] # 返回结果集中的第2-3项
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# 其他高级查询
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user = session.query(User).filter(User.id < 6).first() # 条件查询
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users = session.query(User).order_by(User.name) # 排序查询
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users = session.query(User).order_by(sqlalchemy.desc(User.name)) # 排序查询之倒序
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users = session.query(User.id, User.name) # 只查询部分属性
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users = session.query(User.name.label("user_name")).all() # 给结果集的列取别名
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for user in users: print(user.user_name) # 这里使用别名
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users = session.query(sqlalchemy.distinct(User.name)).all() # 去重查询
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user_count = session.query(User.name).count() # 统计全部数量
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age_avg = session.query(sqlalchemy.func.avg(User.age)).first() # 求平均值
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age_sum = session.query(sqlalchemy.func.sum(User.age)).first() # 求和运算
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users = session.query(sqlalchemy.func.count(User.name).label("count"), User.age).group_by(User.age) # 分组查询
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for user in users:
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print("age:{0}, count:{1}".format(user.age, user.count))
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except Exception as excep:
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session.rollback()
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raise
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