以下這段代碼的default怎么理解，是有個參數(shù)為default嗎？那么這個default有什么用途呢？我是從c#轉(zhuǎn)來學(xué)python的，看到這個函數(shù)覺得很奇怪，覺得default是多余的。（代碼是從開源程序中copy來的）defpretty_date(dt,default=None):"""Returnsstringrepresenting"timesince"e.g.3daysago,5hoursagoetc."""ifdefaultisNone:default='justnow'now=datetime.utcnow()diff=now-dtperiods=((diff.days/365,'year','years'),(diff.days/30,'month','months'),(diff.days/7,'week','weeks'),(diff.days,'day','days'),(diff.seconds/3600,'hour','hours'),(diff.seconds/60,'minute','minutes'),(diff.seconds,'second','seconds'),)forperiod,singular,pluralinperiods:ifnotperiod:continueifperiod==1:returnu'%d%sago'%(period,singular)else:returnu'%d%sago'%(period,plural)returndefault