路易吉任务去哪了？

Question

这是我第一次接触Luigi（还有Python！），有一些问题想请教。相关的代码如下：

from Database import Database
import luigi

class bbSanityCheck(luigi.Task):

  conn = luigi.Parameter()
  date = luigi.Parameter()
  def __init__(self, *args, **kwargs):
    super(bbSanityCheck, self).__init__(*args, **kwargs)
    self.has_run = False

  def run(self):
    print "Entering run of bb sanity check"
    # DB STUFF HERE THAT DOESN"T MATTER
   print "Are we in la-la land?"

  def complete(self):
    print "BB Sanity check being asked for completeness: " , self.has_run
    return self.has_run

class Pipeline(luigi.Task):
  date = luigi.DateParameter()

  def requires(self):
    db = Database('cbs')
    self.conn = db.connect()
    print "I'm about to yield!"
    return bbSanityCheck(conn = self.conn, date = self.date)


  def run(self):
    print "Hello World"
    self.conn.query("""SELECT * 
              FROM log_blackbook""")
    result = conn.store_result()

    print result.fetch_row()

  def complete(self):
    return False

if __name__=='__main__':
  luigi.run()

输出结果在这里（相关的数据库返回信息已删去）：

DEBUG: Checking if Pipeline(date=2013-03-03) is complete
I'm about to yield!
INFO: Scheduled Pipeline(date=2013-03-03)
I'm about to yield!
DEBUG: Checking if bbSanityCheck(conn=<_mysql.connection open to 'sas1.rad.wc.truecarcorp.com' at 223f050>, date=2013-03-03) is complete
BB Sanity check being asked for completeness:  False
INFO: Scheduled bbSanityCheck(conn=<_mysql.connection open to 'sas1.rad.wc.truecarcorp.com' at 223f050>, date=2013-03-03)
INFO: Done scheduling tasks
DEBUG: Asking scheduler for work...
DEBUG: Pending tasks: 2
INFO: [pid 5150] Running   bbSanityCheck(conn=<_mysql.connection open to 'sas1.rad.wc.truecarcorp.com' at 223f050>, date=2013-03-03)
Entering run of bb sanity check
Are we in la-la land?
INFO: [pid 5150] Done      bbSanityCheck(conn=<_mysql.connection open to 'sas1.rad.wc.truecarcorp.com' at 223f050>, date=2013-03-03)
DEBUG: Asking scheduler for work...
INFO: Done
INFO: There are no more tasks to run at this time
INFO: There are 1 pending tasks possibly being run by other workers
INFO: Worker was stopped. Shutting down Keep-Alive thread

所以我的问题是：

1.) 为什么“我快要输出了”会打印两次？

2.) 为什么“你好，世界”从来没有被打印出来？

3.) 什么是“1个待处理任务可能由其他工作者运行”？

我更喜欢输出结果超级干净，因为这样更容易维护。我希望能把这些警告信息搞清楚。

我还注意到需要使用“yield”或者“return item, item2, item3”。我读过关于yield的内容，也理解它的意思。但我不明白的是，这两种写法哪种更好，或者它们之间是否有一些细微的区别，而我作为新手还没有理解。

代码调试数据库交互 yield 任务调度输出管理 return 工作者模型 luigi

路易吉任务去哪了？

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