看一看 MRjob 运行hadoop作业的帮助程序包。为这个任务编写一个map/reduce将是一个相当简单的过程，它可以按照下面的代码行进行

from datetime import datetime
from MRJob import MRJob

class JoinJob(MRJob):
    fmt = '%Y-%M-%d'
    def steps(self):
        return [self.mr(mapper=self.mapper, 
                        reducer=self.reducer)]
    def mapper(self, rec_time, rec_id):
        yield rec_id, rec_time

    def reducer(self, rec_id, datetime_strs):
        datetimes = map(lambda x: datetime.strptime(x, self.fmt), 
                            datetime_strs)
        delta_secs = (max(datetimes) - min(datetimes)).total_seconds()
        yield rec_id, delta_secs

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