http://www.yeayee.com/ 264/531 什么叫“多任务”呢？简单地说，就是操作系统可以同时运行多个任务。 打个比方，你一边在用浏览器上网，一边在听 MP3，一边在用 Word 赶 作业，这就是多任务，至少同时有 3 个任务正在运行。还有很多任务悄 悄地在后台同时运行着，只是桌面上没有显示而已。 现在，多核 CPU 已经非常普及了，但是，即使过去的单核 CPU，也可 以执行多任务。由于 无论是多进程还是多线程，只要数量一多，效率肯定上不去，为什么呢？ 我们打个比方，假设你不幸正在准备中考，每天晚上需要做语文、数学、 英语、物理、化学这 5 科的作业，每项作业耗时 1 小时。 如果你先花 1 小时做语文作业，做完了，再花 1 小时做数学作业，这样， 依次全部做完，一共花 5 小时，这种方式称为单任务模型，或者批处理 任务模型。 假设你打算切换到多任务模型，可以先做 1 分钟语文，再切换到数学作 快，这种 方式就和单核 CPU 执行多任务是一样的了，以幼儿园小朋友的眼光来 看，你就正在同时写 5 科作业。 但是，切换作业是有代价的，比如从语文切到数学，要先收拾桌子上的 语文书本、钢笔（这叫保存现场），然后，打开数学课本、找出圆规直 尺（这叫准备新环境），才能开始做数学作业。操作系统在切换进程或 者线程时也是一样的，它需要先保存当前执行的现场环境（CPU 寄存器 状态、内存页

Thread(target=scheduler_thread) thread.start() schedule.run_all() # 立即运行所有作业 schedule.run_all(delay_seconds=10) # 立即运行所有作业，每次 作业间隔10秒 all_jobs = schedule.get_jobs("jobxx") # 获取指定标签的所有 任务 schedule.clear("jobxx")

i About the Tutorial SQLAlchemy is a popular SQL toolkit and Object Relational Mapper. It is written in Python and gives full power and flexibility of SQL to an application developer cross-platform software released under MIT license. SQLAlchemy is famous for its object-relational mapper (ORM), using which classes can be mapped to the database, thereby allowing the object model and SQLAlchemy 1 SQLAlchemy is a popular SQL toolkit and Object Relational Mapper. It is written in Python and gives full power and flexibility of SQL to an application developer

Flask-SQLAlchemy Extension Because SQLAlchemy is a common database abstraction layer and object relational mapper that requires a little bit of configuration effort, there is a Flask extension that handles that into models.py): from sqlalchemy import Table, Column, Integer, String from sqlalchemy.orm import mapper from yourapplication.database import metadata, db_session class User(object): query = db_session primary_key=True), Column('name', String(50), unique=True), Column('email', String(120), unique=True) ) mapper(User, users) Querying and inserting works exactly the same as in the example above. SQL Abstraction

Flask-SQLAlchemy Extension Because SQLAlchemy is a common database abstraction layer and object relational mapper that requires a little bit of configuration effort, there is a Flask extension that handles that into models.py): from sqlalchemy import Table, Column, Integer, String from sqlalchemy.orm import mapper from yourapplication.database import metadata, db_session class User(object): query = db_session primary_key=True), Column('name', String(50), unique=True), Column('email', String(120), unique=True) ) mapper(User, users) Querying and inserting works exactly the same as in the example above. SQL Abstraction

Design your model Although you can use Django without a database, it comes with an object-relational mapper in which you describe your database layout in Python code. The data-model syntax offers many rich SQL If you find yourself needing to write an SQL query that is too complex for Django’s database-mapper to handle, you can fall back on writing SQL by hand. Django has a couple of options for writing raw (positional, keyword) and values of the view arguments. Django provides a solution such that the URL mapper is the only repository of the URL design. You feed it with your URLconf and then it can be used in

Design your model Although you can use Django without a database, it comes with an object-relational mapper in which you describe your database layout in Python code. The data-model syntax offers many rich SQL If you find yourself needing to write an SQL query that is too complex for Django’s database-mapper to handle, you can fall back on writing SQL by hand. Django has a couple of options for writing raw (positional, keyword) and values of the view arguments. Django provides a solution such that the URL mapper is the only repository of the URL design. You feed it with your URLconf and then it can be used in

Design your model Although you can use Django without a database, it comes with an object-relational mapper in which you describe your database layout in Python code. The data-model syntax offers many rich SQL If you find yourself needing to write an SQL query that is too complex for Django’s database-mapper to handle, you can fall back on writing SQL by hand. Django has a couple of options for writing raw (positional, keyword) and values of the view arguments. Django provides a solution such that the URL mapper is the only repository of the URL design. You feed it with your URLconf and then it can be used in

Design your model Although you can use Django without a database, it comes with an object-relational mapper in which you describe your database layout in Python code. The data-model syntax offers many rich SQL If you find yourself needing to write an SQL query that is too complex for Django’s database-mapper to handle, you can fall back on writing SQL by hand. Django has a couple of options for writing raw (positional, keyword) and values of the view arguments. Django provides a solution such that the URL mapper is the only repository of the URL design. You feed it with your URLconf and then it can be used in

Design your model Although you can use Django without a database, it comes with an object-relational mapper in which you describe your database layout in Python code. The data-model syntax offers many rich SQL If you find yourself needing to write an SQL query that is too complex for Django’s database-mapper to handle, you can fall back on writing SQL by hand. Django has a couple of options for writing raw (positional, keyword) and values of the view arguments. Django provides a solution such that the URL mapper is the only repository of the URL design. You feed it with your URLconf and then it can be used in